Add Appraisal for Rails 4.2
Fix test suite to properly tag example groups

When running unit tests we need to ensure that we are simulating how
other people will use the matchers as best we can. This means, for
instance, tagging any example groups that test controller matchers as
controller example groups.
Ensure that we are req'd after rspec in tests

Currently before running unit tests we are getting auto-required before
rspec-rails is getting required. This is bad because we need to wait
until rspec-rails is loaded before injecting Shoulda::Matchers::* into
the current RSpec context, otherwise matchers that clash with
rspec-rails (such as `render_template` will get overridden).

This is happening when creating and booting the Rails application.
Bundler will auto-require any gems in the Gemfile. One of these gems is
ourselves (via the `gemspec` line). Since there aren't any dependencies
in the gemspec, there's no need for us to be in the Gemfile.

This means that we no longer have to explicit `include` Rails
ActionController template assertions in the tests for `render_template`
as they should get included automatically for us.
Fix AC matcher tests for Rails 4.2

Modify helper methods provided by ControllerBuilder so that we use as
much of rspec-rails's controller example group capabilities as possible.
All of this can still be improved but this is a good start for now.
Ensure that ActiveSupport warnings are being printed during tests
Fix AR matcher tests for Rails 4.2
Remove warning about #capture under 4.2+
Fix acceptance tests where we should be using Bundler
Add NEWS for Rails 4.2 [ci skip]
Bump top supported Ruby version to 2.1.5

[ci skip]
Bump version to 2.8.0.rc1

[ci skip]
Tweak NEWS

[ci skip]
Documentation updates

[ci skip]