Add link_attr option to Autolink filter to allow for adding attributes to links
Merge pull request #89 from excid3/master

Add link_attr option to Autolink filter
Relative link to Gemfile
Merge remote-tracking branch 'upstream/master' into simple-dependency-management
Don't test dependency management since its testing require and is brittle
No need for MissingDependencyException
If a dependency is missing, exit with a 1 status and write help message to STDERR.