Correctly handle blank and nil values when applying auto_html. 

Signed-off-by: Ryan Heneise <ryan@artofmission.com>
Merge branch 'master' of https://github.com/dejan/auto_html into dejan/master
Added a filter for Markdown syntax.
Added another test for markdown filter.
Added an auto link for worldstar hiphop
Added test unit for worldstat
Added a unit test for worldstar
added options to worldstar filter
fixed error with gemfile
Youtube: autoplay option added
hide_related option implemented
Permit auto_html_for on an attribute that's not in the DB.

This makes it possible to declare an aliased attribute in your model, then call auto_html_for with a different set of options.
Adds some regex to the image filter to make sure we don't transform things that are already img tags.

Helpful when using redcarpet in front of the image filter.
Makes sure the twitter filter doesn't format already formatted Twitter blockquotes.

Also adds unit tests for Twitter.
allow a :proxy option on image filter
Add Instagram filters + tests
Fix require list Instagram filter file
Clean up Instagram files
updating the youtube filter regexp to allow <br> tags right after the youtube link, with no whitespace between them
use a static date in gemspec