add note of how to support table with more than 22 fields

Author: wangfei <wangfei1@huawei.com>

Closes #564 from scwf/patch-6 and squashes the following commits:

a331876 [wangfei] Update sql-programming-guide.md
685135b [wangfei] Update sql-programming-guide.md
10b3dc0 [wangfei] Update sql-programming-guide.md
1c40480 [wangfei] add note of how to support table with 22 fields
[SPARK-1608] [SQL] Fix Cast.nullable when cast from StringType to NumericType/TimestampType.

`Cast.nullable` should be `true` when cast from `StringType` to `NumericType` or `TimestampType`.
Because if `StringType` expression has an illegal number string or illegal timestamp string, the casted value becomes `null`.

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

Closes #532 from ueshin/issues/SPARK-1608 and squashes the following commits:

065d37c [Takuya UESHIN] Add tests to check nullabilities of cast expressions.
f278ed7 [Takuya UESHIN] Revert test to keep it readable and concise.
9fc9380 [Takuya UESHIN] Fix Cast.nullable when cast from StringType to NumericType/TimestampType.
SPARK-1467: Make StorageLevel.apply() factory methods Developer APIs

We may want to evolve these in the future to add things like SSDs, so let's mark them as experimental for now. Long-term the right solution might be some kind of builder. The stable API should be the existing StorageLevel constants.

Author: Sandeep <sandeep@techaddict.me>

Closes #551 from techaddict/SPARK-1467 and squashes the following commits:

6bdda24 [Sandeep] SPARK-1467: Make StorageLevel.apply() factory methods as Developer Api's We may want to evolve these in the future to add things like SSDs, so let's mark them as experimental for now. Long-term the right solution might be some kind of builder. The stable API should be the existing StorageLevel constants.
SPARK-1606: Infer user application arguments instead of requiring --arg.

This modifies spark-submit to do something more like the Hadoop `jar`
command. Now we have the following syntax:

./bin/spark-submit [options] user.jar [user options]

Author: Patrick Wendell <pwendell@gmail.com>

Closes #563 from pwendell/spark-submit and squashes the following commits:

32241fc [Patrick Wendell] Review feedback
3adfb69 [Patrick Wendell] Small fix
bc48139 [Patrick Wendell] SPARK-1606: Infer user application arguments instead of requiring --arg.