[Docs] SQL doc formatting and typo fixes

As [reported on the dev list](http://apache-spark-developers-list.1001551.n3.nabble.com/VOTE-Release-Apache-Spark-1-1-0-RC2-tp8107p8131.html):
* Code fencing with triple-backticks doesn’t seem to work like it does on GitHub. Newlines are lost. Instead, use 4-space indent to format small code blocks.
* Nested bullets need 2 leading spaces, not 1.
* Spellcheck!

Author: Nicholas Chammas <nicholas.chammas@gmail.com>
Author: nchammas <nicholas.chammas@gmail.com>

Closes #2201 from nchammas/sql-doc-fixes and squashes the following commits:

873f889 [Nicholas Chammas] [Docs] fix skip-api flag
5195e0c [Nicholas Chammas] [Docs] SQL doc formatting and typo fixes
3b26c8d [nchammas] [Spark QA] Link to console output on test time out
SPARK-2813:  [SQL] Implement SQRT() directly in Spark SQL

This PR adds a native implementation for SQL SQRT() and thus avoids delegating this function to Hive.

Author: William Benton <willb@redhat.com>

Closes #1750 from willb/spark-2813 and squashes the following commits:

22c8a79 [William Benton] Fixed missed newline from rebase
d673861 [William Benton] Added string coercions for SQRT and associated test case
e125df4 [William Benton] Added ExpressionEvaluationSuite test cases for SQRT
7b84bcd [William Benton] SQL SQRT now properly returns NULL for NULL inputs
8256971 [William Benton] added SQRT test to SqlQuerySuite
504d2e5 [William Benton] Added native SQRT implementation