Add contribution guidelines
[#23] Added Swift as a contributor in the gemspec.

Fixes #23
Merge pull request #24 from thoughtbot/ms-update-gemspec-contributors

[#23] Added Swift as a contributor in the gemspec.
Markdownify thoughtbot CONTRIBUTING
Merge pull request #19 from thoughtbot/ct-contributing

Add contribution guidelines
Use body_from_email helper in all tests
Don't assume every email is binary. If charset is set, set src encoding to charset
Replaced symbols with string to match the actual hash that Sendgrid uses. Added theycallmeswift feedback
In test, store mail body text with real encoding but say is utf-8
Changed copy of a test title and replaced return with if/else
Added space around the =
Allow for some console hacking

Make `bundle console` and `irb -Ilib -rgriddler` work as expected.
Merge pull request #26 from eval/bundle-console

Allow for some console hacking
Merge pull request #27 from innku/em_dont_assume_encoding_binary

Dont assume mail body text encoding is binary
Mock out what adapters should look like
Extract email provider responsibilities to adapter

Sendgrid posts with a particular format to their params. As will every
other service. We introduce a manner of transforming all of those params
formats into one consistent, common `params` object via an email service
specific adapter. Right now SendGrid is the only service supported in
this PR but this will provide a common interface for future providers to
be more easily added in.

* "massage" params from provider in controller to common format
* Create SendGrid adapter
* SendGrid adapter now changes how attachments are represented - as an array
* Raise an error if configuration is requesting an adapter that doesn't exist
Clean up in various places

* Use one loop instead of two in sendgrid_adapter
* sendgrid not send_grid
[JRO] Clean up the SendGrid adapter class
[JRO] Renaming classes, rebasing

* sendgrid_adapter.rb => SendgridAdapter, not SendGridAdapter
[JRO] Pull req feedback

Thanks to comments from @gabebw and @calebthompson