Updated version.txt and release notes for Gradle 2.1
GRADLE-902 Adds ANTLR v3 support to existing antlr plugin.
Define some terminology.
Some work on mapping out how plugins {} can be used to use non-isolated plugins.
Add notes about handling of old and new plugin style plugins through old and new mechanisms.

 These will be turned into detail soon.
Remove some terminology that no longer holds.

No replacement at this stage.
Merge branch 'release'
Remove answered open question.
Update spec with new strategy for backwards/forwards compatibilty of plugins and plugin loading mechanisms.
Merge branch 'release'

Conflicts:
	subprojects/docs/src/docs/release/notes.md
Add story for loading old style plugin through plugins {}.
Restructure spec to accommodate for change in focus towards making as-is plugins work via plugins {}.
Updated implemented test coverage.
Move “resolve all plugins before applying any” story into milestone 1.
Use “plugin resolution service” instead of “plugin portal”.
Add a little detail to the forward/backward compatibility section, and schedule some more stories for these concerns.
Focus test on communication aspects of using the plugin resolution service.
Rework the PluginResolver API to support more complex outcomes.
Suitable message when declaring non core plugin dependency without version number.
Remove answered open question.