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
Arrows to display the previous and next files.
Merge commit 'ec05c0eaf7060d13a23828c0c2e64137dde4bd61' into feature-restapi
Merge commit '4891aa79bf80d5f6f1a50d71e43b3eb49cc1fe85' into feature-restapi
rest api WIP
test break fix.
fixes #2559
fix formatting
fix formatting
Merge remote-tracking branch 'origin/2559-pjax-filter' into 2559-pjax-filter

* origin/2559-pjax-filter:
  fix formatting
Add $transliteration for Vietnamese

Please review and merge it,
Thank advance
Fixed incorrect error handling.
add multiple grid support to gridData
typo fix.
Fixes #2601