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.
Add Instagram filters + tests
Fix require list Instagram filter file
Clean up Instagram files
Merge branch 'master' of https://github.com/dejan/auto_html
Image filter should only transform text if it is preceded by a newline or whitespace. (Won't transform images already wrapped in an <img> tag.)
Fixed markdown test.
Removing Markdown filter as redundant to Redcarpet
Updating Instagram embed code to use /embed
Fixing formatting of URL
Fixing Get of instagram embed
Revert 9cd0d60..c7177f8

This rolls back to commit 9cd0d60f2034fbfb8c1f5c1aca550abc942763fe.
Merge pull for instagram support

From - https://github.com/Dhaulagiri/auto_html
Pull fix for image filter. Doesn't re-wrap images already in tags.

From https://github.com/mysmallidea/auto_html