[ci skip] Document PublicExceptions middleware
[ci skip] document ActionDispatch::FileHandler
[ci skip] Document ActionDispatch::Static
Uppercase HTML in docs.

[skip ci]
`overriden` => `overridden`
[ci skip] Update links in getting_started guide.
Merge branch 'master' of github.com:rails/docrails

Conflicts:
	actionpack/lib/action_controller/metal/mime_responds.rb
	actionview/lib/action_view/vendor/html-scanner/html/sanitizer.rb
	activerecord/lib/active_record/type/value.rb