SPARK-971 [DOCS] Link to Confluence wiki from project website / documentation

This is a trivial change to add links to the wiki from `README.md` and the main docs page. It is already linked to from spark.apache.org.

Author: Sean Owen <sowen@cloudera.com>

Closes #3169 from srowen/SPARK-971 and squashes the following commits:

dcb84d0 [Sean Owen] Add link to wiki from README, docs home page

(cherry picked from commit 8c99a47a4f0369ff3c1ecaeb860fa61ee789e987)
Signed-off-by: Patrick Wendell <pwendell@gmail.com>
SPARK-1344 [DOCS] Scala API docs for top methods

Use "k" in javadoc of top and takeOrdered to avoid confusion with type K in pair RDDs. I think this resolves the discussion in SPARK-1344.

Author: Sean Owen <sowen@cloudera.com>

Closes #3168 from srowen/SPARK-1344 and squashes the following commits:

6963fcc [Sean Owen] Use "k" in javadoc of top and takeOrdered to avoid confusion with type K in pair RDDs

(cherry picked from commit d1362659ef5d62db2c9ff0d2a24639abcef4e118)
Signed-off-by: Patrick Wendell <pwendell@gmail.com>
SPARK-1209 [CORE] (Take 2) SparkHadoop{MapRed,MapReduce}Util should not use package org.apache.hadoop

andrewor14 Another try at SPARK-1209, to address https://github.com/apache/spark/pull/2814#issuecomment-61197619

I successfully tested with `mvn -Dhadoop.version=1.0.4 -DskipTests clean package; mvn -Dhadoop.version=1.0.4 test` I assume that is what failed Jenkins last time. I also tried `-Dhadoop.version1.2.1` and `-Phadoop-2.4 -Pyarn -Phive` for more coverage.

So this is why the class was put in `org.apache.hadoop` to begin with, I assume. One option is to leave this as-is for now and move it only when Hadoop 1.0.x support goes away.

This is the other option, which adds a call to force the constructor to be public at run-time. It's probably less surprising than putting Spark code in `org.apache.hadoop`, but, does involve reflection. A `SecurityManager` might forbid this, but it would forbid a lot of stuff Spark does. This would also only affect Hadoop 1.0.x it seems.

Author: Sean Owen <sowen@cloudera.com>

Closes #3048 from srowen/SPARK-1209 and squashes the following commits:

0d48f4b [Sean Owen] For Hadoop 1.0.x, make certain constructors public, which were public in later versions
466e179 [Sean Owen] Disable MIMA warnings resulting from moving the class -- this was also part of the PairRDDFunctions type hierarchy though?
eb61820 [Sean Owen] Move SparkHadoopMapRedUtil / SparkHadoopMapReduceUtil from org.apache.hadoop to org.apache.spark

(cherry picked from commit f8e5732307dcb1482d9bcf1162a1090ef9a7b913)
Signed-off-by: Patrick Wendell <pwendell@gmail.com>
SPARK-3179. Add task OutputMetrics.

Author: Sandy Ryza <sandy@cloudera.com>

This patch had conflicts when merged, resolved by
Committer: Kay Ousterhout <kayousterhout@gmail.com>

Closes #2968 from sryza/sandy-spark-3179 and squashes the following commits:

dce4784 [Sandy Ryza] More review feedback
8d350d1 [Sandy Ryza] Fix test against Hadoop 2.5+
e7c74d0 [Sandy Ryza] More review feedback
6cff9c4 [Sandy Ryza] Review feedback
fb2dde0 [Sandy Ryza] SPARK-3179

(cherry picked from commit 3c2cff4b9464f8d7535564fcd194631a8e5bb0a5)
Signed-off-by: Kay Ousterhout <kayousterhout@gmail.com>
[SPARK-2703][Core]Make Tachyon related unit tests execute without deploying a Tachyon system locally.

Make Tachyon related unit tests execute without deploying a Tachyon system locally.

Author: RongGu <gurongwalker@gmail.com>

Closes #3030 from RongGu/SPARK-2703 and squashes the following commits:

ad08827 [RongGu] Make Tachyon related unit tests execute without deploying a Tachyon system locally

(cherry picked from commit bd86cb1738800a0aa4c88b9afdba2f97ac6cbf25)
Signed-off-by: Patrick Wendell <pwendell@gmail.com>