Added more guide sections
Fixes #753: fixed sorting issue of ActiveDataProvider
Reorganized application template docs structure
basic application usage guide
started advanced application guide
more on advanced app docs
css fixes.
Merge branch 'master' of github.com:yiisoft/yii2
docs on configuring Yii
Added default value of Validator::attributes.
Merge branch 'master' of github.com:yiisoft/yii2
started view docs
Added Installation part to app template docs
started bootstrap docs
Fixes #756: added doc to Dropdown.
explained why AR is used in an example for scenarios  doc
fixed extension documentation
Added Html::error().
Update apps-basic.md

update path document root
Update apps-advanced.md

document roots and composer folder params