fix Enumerator.scala scaladoc
Add environment variable 'PLAY_OPTS' to be able to configure system properties in Play.

With PLAY_OPTS, we can override JVM parameters, SBT configuration ... without any modification in Play's scripts.

See also https://github.com/playframework/Play20/pull/1184
Wrap PLAY_OPTS in %ENV_VAR%
Scaladoc Fix
Removed duplication
Extracted methods for readability.
Some minor improvements
Applied scalariform
 #1257 Extracted doc processing out of Play
Merge pull request #1257 from jroper/1257-doc-extract

Prep website for new documentation format
Merge pull request #1301 from tototoshi/refactoring-evolutions

Refactoring evolutions
Merge pull request #1258 from wsargent/JVM-environment-variables

Add environment variable 'PLAY_OPTS' to 'play' and 'play.bat' scripts
Merge pull request #1202 from xuwei-k/fix-Enumerator-scaladoc

fix Enumerator.scala scaladoc
Merge pull request #1242 from jroper/1242-jsnull

Json.parse("null") returns null instead of JsNull
Merge pull request #1240 from jroper/1240-media-range-slashes

[2.1.1-scala] MediaRange implementation assumes that there is no additional "/" except range separator.
Merge pull request #1245 from jroper/results-refactor-keep-alive

Switch to keep-alive flag with chunking done in Play
#1305 Started 2.2 migration guide and highlights
Fix package script for 2.2 milestone release