refactored apidoc extensions completely.

separated guide and apidoc, better maintainability
replaced keyword "yii" with "yii2" in composer.json files (fixes #2557)
rest WIP
Merge commit 'd3ff343e5ee02a14dd17d6cf947aa7f52857474a' into feature-restapi

Conflicts:
	framework/helpers/BaseArrayHelper.php
Merge commit '24e086deaf6336706624e77cc0f63a7062280821' into feature-restapi
rest WIP
fix doc code according to yii2 core code style (When instantiating class it should be new MyClass(); instead of new MyClass;.)
raised dependency for phpdocumentor docblock lib

in this version a bug that affects markdown display has been fixed.

fixes #2589
Merge pull request #2591 from AlexGx/doc-codestyle-fix

fix doc code according to yii2 core code style
run build against PHP5.6 and hhvm but allow to fail

http://docs.travis-ci.com/user/build-configuration/#Rows-That-are-Allowed-To-Fail
Delay joinWith till createCommand to correctly combine relation condition with primary condition.
fixed test break.
typo fix.
Arrows to display the previous and next files.
Fixes #1535: Improved `yii\web\User` to start session only when needed. Also prepared it for use without session.
Merge commit 'ec05c0eaf7060d13a23828c0c2e64137dde4bd61' into feature-restapi
Merge commit '4891aa79bf80d5f6f1a50d71e43b3eb49cc1fe85' into feature-restapi
rest api WIP
test break fix.
fixes #2559