Snippet fixes, including:

– Escaped slashes in URIs which don't need to be escaped (in ST3?)
- Replace instances of %0 which should actually be $0
- Proper closing tag in figcaption snippet (was </figure>)
- Proper indentation in <ul> in <nav> snippet
Add new snippet for <main> element.

Patterned after the <article> element, thus placed in the same
snippet subdirectory.
Merge pull request #13 from yellowled/master

Thank you for your efforts @yellowled.