Added '.raw_text' and '.raw_html' to Email

Griddler::Email only supported '.raw_body', which doesn't allow access to both the text and the html of the email easily. Added '.raw_text' and '.raw_html' methods.
Add specs for Email#raw_text and #raw_html
Add specs for raw_body
Merge pull request #50 from brentd/raw_html

Add Email#raw_html and #raw_text