[DOCS][SQL] Add a Note on jsonFile having separate JSON objects per line

* This commit hopes to avoid the confusion I faced when trying
  to submit a regular, valid multi-line JSON file, also see

  http://apache-spark-user-list.1001560.n3.nabble.com/Loading-JSON-Dataset-fails-with-com-fasterxml-jackson-databind-JsonMappingException-td20041.html

Author: Peter Vandenabeele <peter@vandenabeele.com>

Closes #3517 from petervandenabeele/pv-docs-note-on-jsonFile-format/01 and squashes the following commits:

1f98e52 [Peter Vandenabeele] Revert to people.json and simple Note text
6b6e062 [Peter Vandenabeele] Change the "JSON" connotation to "txt"
fca7dfb [Peter Vandenabeele] Add a Note on jsonFile having separate JSON objects per line
[SPARK-4847][SQL]Fix "extraStrategies cannot take effect in SQLContext" issue

Author: jerryshao <saisai.shao@intel.com>

Closes #3698 from jerryshao/SPARK-4847 and squashes the following commits:

4741130 [jerryshao] Make later added extraStrategies effect when calling strategies
[SPARK-4812][SQL] Fix the initialization issue of 'codegenEnabled'

The problem is `codegenEnabled` is `val`, but it uses a `val` `sqlContext`, which can be override by subclasses. Here is a simple example to show this issue.

```Scala
scala> :paste
// Entering paste mode (ctrl-D to finish)

abstract class Foo {

  protected val sqlContext = "Foo"

  val codegenEnabled: Boolean = {
    println(sqlContext) // it will call subclass's `sqlContext` which has not yet been initialized.
    if (sqlContext != null) {
      true
    } else {
      false
    }
  }
}

class Bar extends Foo {
  override val sqlContext = "Bar"
}

println(new Bar().codegenEnabled)

// Exiting paste mode, now interpreting.

null
false
defined class Foo
defined class Bar
```

We should make `sqlContext` `final` to prevent subclasses from overriding it incorrectly.

Author: zsxwing <zsxwing@gmail.com>

Closes #3660 from zsxwing/SPARK-4812 and squashes the following commits:

1cbb623 [zsxwing] Make `sqlContext` final to prevent subclasses from overriding it incorrectly
SPARK-4767: Add support for launching in a specified placement group to spark_ec2

Placement groups are cool and all the cool kids are using them. Lets add support for them to spark_ec2.py because I'm lazy

Author: Holden Karau <holden@pigscanfly.ca>

Closes #3623 from holdenk/SPARK-4767-add-support-for-launching-in-a-specified-placement-group-to-spark-ec2-scripts and squashes the following commits:

111a5fd [Holden Karau] merge in master
70ace25 [Holden Karau] Placement groups are cool and all the cool kids are using them. Lets add support for them to spark_ec2.py because I'm lazy
[SPARK-4527][SQl]Add BroadcastNestedLoopJoin operator selection testsuite

In `JoinSuite` add BroadcastNestedLoopJoin operator selection testsuite

Author: wangxiaojing <u9jing@gmail.com>

Closes #3395 from wangxiaojing/SPARK-4527 and squashes the following commits:

ea0e495 [wangxiaojing] change style
53c3952 [wangxiaojing] Add BroadcastNestedLoopJoin operator selection testsuite
[SPARK-4483][SQL]Optimization about reduce memory costs during the HashOuterJoin

In `HashOuterJoin.scala`, spark read data from both side of join operation before zip them together. It is a waste for memory. We are trying to read data from only one side, put them into a hashmap, and then generate the `JoinedRow` with data from other side one by one.
Currently, we could only do this optimization for `left outer join` and `right outer join`. For `full outer join`, we will do something in another issue.

for
table test_csv contains 1 million records
table dim_csv contains 10 thousand records

SQL:
`select * from test_csv a left outer join dim_csv b on a.key = b.key`

the result is:
master:
```
CSV: 12671 ms
CSV: 9021 ms
CSV: 9200 ms
Current Mem Usage:787788984
```
after patch：
```
CSV: 10382 ms
CSV: 7543 ms
CSV: 7469 ms
Current Mem Usage:208145728
```

Author: tianyi <tianyi@asiainfo-linkage.com>
Author: tianyi <tianyi.asiainfo@gmail.com>

Closes #3375 from tianyi/SPARK-4483 and squashes the following commits:

72a8aec [tianyi] avoid having mutable state stored inside of the task
99c5c97 [tianyi] performance optimization
d2f94d7 [tianyi] fix bug: missing output when the join-key is null.
2be45d1 [tianyi] fix spell bug
1f2c6f1 [tianyi] remove commented codes
a676de6 [tianyi] optimize some codes
9e7d5b5 [tianyi] remove commented old codes
838707d [tianyi] Optimization about reduce memory costs during the HashOuterJoin
[SPARK-4827][SQL] Fix resolution of deeply nested Project(attr, Project(Star,...)).

Since `AttributeReference` resolution and `*` expansion are currently in separate rules, each pair requires a full iteration instead of being able to resolve in a single pass.  Since its pretty easy to construct queries that have many of these in a row, I combine them into a single rule in this PR.

Author: Michael Armbrust <michael@databricks.com>

Closes #3674 from marmbrus/projectStars and squashes the following commits:

d83d6a1 [Michael Armbrust] Fix resolution of deeply nested Project(attr, Project(Star,...)).
[SPARK-4269][SQL] make wait time configurable in BroadcastHashJoin

In BroadcastHashJoin, currently it is using a hard coded value (5 minutes) to wait for the execution and broadcast of the small table.
In my opinion, it should be a configurable value since broadcast may exceed 5 minutes in some case, like in a busy/congested network environment.

Author: Jacky Li <jacky.likun@huawei.com>

Closes #3133 from jackylk/timeout-config and squashes the following commits:

733ac08 [Jacky Li] add spark.sql.broadcastTimeout in SQLConf.scala
557acd4 [Jacky Li] switch to sqlContext.getConf
81a5e20 [Jacky Li] make wait time configurable in BroadcastHashJoin
[Release] Major improvements to generate contributors script

This commit introduces several major improvements to the script
that generates the contributors list for release notes, notably:

(1) Use release tags instead of a range of commits. Across branches,
commits are not actually strictly two-dimensional, and so it is not
sufficient to specify a start hash and an end hash. Otherwise, we
end up counting commits that were already merged in an older branch.

(2) Match PR numbers in addition to commit hashes. This is related
to the first point in that if a PR is already merged in an older
minor release tag, it should be filtered out here. This requires us
to do some intelligent regex parsing on the commit description in
addition to just relying on the GitHub API.

(3) Relax author validity check. The old code fails on a name that
has many middle names, for instance. The test was just too strict.

(4) Use GitHub authentication. This allows us to make far more
requests through the GitHub API than before (5000 as opposed to 60
per hour).

(5) Translate from Github username, not commit author name. This is
important because the commit author name is not always configured
correctly by the user. For instance, the username "falaki" used to
resolve to just "Hossein", which was treated as a github username
and translated to something else that is completely arbitrary.

(6) Add an option to use the untranslated name. If there is not
a satisfactory candidate to replace the untranslated name with,
at least allow the user to not translate it.
[Release] Cache known author translations locally

This bypasses unnecessary calls to the Github and JIRA API.
Additionally, having a local cache allows us to remember names
that we had to manually discover ourselves.
[SPARK-4798][SQL] A new set of Parquet testing API and test suites

This PR provides a set Parquet testing API (see trait `ParquetTest`) that enables developers to write more concise test cases. A new set of Parquet test suites built upon this API  are added and aim to replace the old `ParquetQuerySuite`. To avoid potential merge conflicts, old testing code are not removed yet. The following classes can be safely removed after most Parquet related PRs are handled:

- `ParquetQuerySuite`
- `ParquetTestData`

<!-- Reviewable:start -->
[<img src="https://reviewable.io/review_button.png" height=40 alt="Review on Reviewable"/>](https://reviewable.io/reviews/apache/spark/3644)
<!-- Reviewable:end -->

Author: Cheng Lian <lian@databricks.com>

Closes #3644 from liancheng/parquet-tests and squashes the following commits:

800e745 [Cheng Lian] Enforces ordering of test output
3bb8731 [Cheng Lian] Refactors HiveParquetSuite
aa2cb2e [Cheng Lian] Decouples ParquetTest and TestSQLContext
7b43a68 [Cheng Lian] Updates ParquetTest Scaladoc
7f07af0 [Cheng Lian] Adds a new set of Parquet test suites
[SPARK-4744] [SQL] Short circuit evaluation for AND & OR in CodeGen

Author: Cheng Hao <hao.cheng@intel.com>

Closes #3606 from chenghao-intel/codegen_short_circuit and squashes the following commits:

f466303 [Cheng Hao] short circuit for AND & OR
[SPARK-4720][SQL] Remainder should also return null if the divider is 0.

This is a follow-up of SPARK-4593 (#3443).

Author: Takuya UESHIN <ueshin@happy-camper.st>

Closes #3581 from ueshin/issues/SPARK-4720 and squashes the following commits:

c3959d4 [Takuya UESHIN] Make Remainder return null if the divider is 0.
[SPARK-4375] [SQL] Add 0 argument support for udf

Author: Cheng Hao <hao.cheng@intel.com>

Closes #3595 from chenghao-intel/udf0 and squashes the following commits:

a858973 [Cheng Hao] Add 0 arguments support for udf
[SPARK-4866] support StructType as key in MapType

This PR brings support of using StructType(and other hashable types) as key in MapType.

Author: Davies Liu <davies@databricks.com>

Closes #3714 from davies/fix_struct_in_map and squashes the following commits:

68585d7 [Davies Liu] fix primitive types in MapType
9601534 [Davies Liu] support StructType as key in MapType
[SPARK-4618][SQL] Make foreign DDL commands options case-insensitive

Using lowercase for ```options``` key to make it case-insensitive, then we should use lower case to get value from parameters.
So flowing cmd work
```
      create temporary table normal_parquet
      USING org.apache.spark.sql.parquet
      OPTIONS (
        PATH '/xxx/data'
      )
```

Author: scwf <wangfei1@huawei.com>
Author: wangfei <wangfei1@huawei.com>

Closes #3470 from scwf/ddl-ulcase and squashes the following commits:

ae78509 [scwf] address comments
8f4f585 [wangfei] address comments
3c132ef [scwf] minor fix
a0fc20b [scwf] Merge branch 'master' of https://github.com/apache/spark into ddl-ulcase
4f86401 [scwf] adding CaseInsensitiveMap
e244e8d [wangfei] using lower case in json
e0cb017 [wangfei] make options in-casesensitive
[Release] Update contributors list format and sort it

Additionally, we now warn the user when a duplicate author name
arises, in which case he/she needs to resolve it manually.
[HOTFIX] Fix RAT exclusion for known_translations file

Author: Josh Rosen <joshrosen@databricks.com>

Closes #3719 from JoshRosen/rat-fix and squashes the following commits:

1542886 [Josh Rosen] [HOTFIX] Fix RAT exclusion for known_translations file