refactored apidoc extensions completely.

separated guide and apidoc, better maintainability
replaced keyword "yii" with "yii2" in composer.json files (fixes #2557)
Query::queryScalar wasn't making SELECT DISTINCT queries subqueries
Fix for logic Query::queryScalar uses to check for SELECT DISTINCT
Added support for reading page size from query parameters by `Pagination`
Merge branch 'master' of git://github.com/yiisoft/yii2
Merge pull request #2581 from jom/query-scalar-fix

SELECT DISTINCT queries made subqueries in Query::queryScalar
Improved page size and page number validation.
try to fix test break.
rest WIP
fixed test break
Added relational link tags to LinkPager widget

for prev, next, first and last page.
http://www.w3.org/TR/html401/struct/links.html#h-12.1.2
make registering of link tags optional in LinkPager
Added verb filter to advanced app logout
fixed links in elasticsearch README
apidoc style and typo
fixed apidoc table style
Added `yii\web\UrlRuleInterface` and `yii\web\CompositeUrlRule`
Merge commit 'd3ff343e5ee02a14dd17d6cf947aa7f52857474a' into feature-restapi

Conflicts:
	framework/helpers/BaseArrayHelper.php
Merge commit '24e086deaf6336706624e77cc0f63a7062280821' into feature-restapi