Twig: added path() function, exposed app and this in templates
Smarty: added path function and exposed $app and $this
form wip
Merge branch 'master' of git.yiisoft.com:yii2
added missing init() method to Cache class
Merge branch 'master' of git.yiisoft.com:yii2

* 'master' of git.yiisoft.com:yii2:
  Smarty: added path function and exposed $app and $this
  Twig: added path() function, exposed app and this in templates
Added Json and JsonExpression.
Merge branch 'master' of git.yiisoft.com:yii2
Renamed JsonExpression to JsExpression.
form wip
form wip
better documentation for php expressions

related to issue yiisoft/yii#1921
Explain what a php expression is an refer to the php manual for more
details.
form wip
form fix.
Added ExpressionDependency::data.
Finished js validation for compare validator.
Finished js validation for email and regular expression validators.
Finished js validation for URL validator.
Finished js validation for string validator.
Finished js validation for number validator.