Ref #12 - ActionMailer support beginnings

- Basic mailer in place for testing
Ref #12 - Added tasks file to require path
Ref #12 - Trying to add rake tasks to load path
Ref #12 - Reworked defaults

- Moves the defaults into lib/how_slow/setup.rb
- Reworked the documentation for the HowSlow::Mailer::metrics_email method
- Version bump to expected version
Ref #12 - Corrected some syntax errors
Ref 12 - Moved generation of email metric strings

- Move the generation of email metric strings for the view into their own
  methods and added documentation for them
Ref #12 - Fixed syntax error - extraneous }
Ref #12 - Cleaned up docs and a little code
Ref #12 - Barely working mailer

- Moved the views into app/views
- Changed the Railtie into an Engine in order to get the views to mount in the
  proper place in a consuming app without any futher trouble
- Updated the defaults for configuration :email_options
- Added the view for the default mailer
Ref #12 - Tweaks to fix tests

- Got the existing tests passing
- Changed the default email subject line
- Added a line to require action_mailer, which is required for the tests
- Other small changes
Ref #12 - Added tests to cover defaults
Merge branch 'master' into 12-mailer
Added travis build command.