[Issue #285] Add a way to ignore certain sgml tags while searching for
closing.  Fix bug with backward motion and tag name being too long.
Auto-escape ' inside single-quoted strings.

Given the following text in a buffer, with | representing the cursor:

    'foo|bar'

Then pressing ' should give the following result:

    'foo\'|\'bar'

This is a part fix to Fuco1/smartparens#77.
Merge pull request #281 from Wilfred/master

Auto-escape ' inside single-quoted strings.