Support numeric single quote html entity.

Slim does this by default.
`<translate>`

Support extraction from `<translate>` element. Closes #6.
Add support for Rails' erb templates
Add ERB test
Merge pull request #54 from gabegorelick/erb

Ruby ERB support
Merge pull request #53 from gabegorelick/translate-element

Support extraction from <translate> elements
Merge pull request #9 from neoeno/master

Support numeric single quote html entity.