Document JoinTable migration generator
Update documentation for yml usage

Update documentation for yml usage against https://github.com/rails/rails/issues/8612
Update guides/source/layouts_and_rendering.md

Removed first slash. The subdirectory will nto be found with slash befor it.

fixed inconsistent `require 'test_helper'` in testing guide
Update guides/source/rails_on_rack.md

Rack::Lock actually sets rack.multithread to `false`, not `true`.

Presumably because once inside the mutex, the app can function as if it were single threaded.
Add source extract to detailed exception page
Styling for exception page
Add new style to Routing Error page
Improve line-height to have better line spacing in exception message
Add style to AV::Template::Error exception page
Fix test for DebugExceptions due to template change
Summary and Details HTML elements aren't supported in all modern browsers
formatted_code_for should be private
Add documentation for the TimeWithZone#dst? method.

[ci skip]
Add documentation for TimeWithZone methods
Merge pull request #8668 from guilleiguaran/exceptions

New exceptions pages for development
Improve English

* Fix one error
* Improve wording
* Improve punctuation
Merge pull request #123 from m-o/master

Fixed typo one line in layouts and rendering: stylesheet_link_tag for file in subdirectory.
copy edits [ci skip]
Merge branch 'master' of github.com:lifo/docrails