Add an Email field type

[zackkatz]

Used the LinkField to render an email and found it rather odious to set up properly. It'd be nice to have an actual field type.

The EmailField field type would extend LinkField and would

• Automatically prefix mailto: to the URL values.
• Support ->cc(), ->bcc(), ->subject(), ->body() methods that match to the mailto: link syntax
• Auto-convert line breaks to %0A, spaces with %20