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
Merge pull request #760 from lancecoder/patch-4

Update apps-advanced.md
Merge pull request #759 from lancecoder/patch-3

Update apps-basic.md
Update installation.md
Merge pull request #761 from lancecoder/patch-5

Update installation.md
Update caching.md
Merge pull request #762 from lancecoder/patch-6

Update caching.md
Fixes #763: handling empty string for date formatting.
Add RegularExpressionValidatorTest
Merge remote-tracking branch 'upstream/master' into add-tests