Use new grunt files API.
Remove unnecessary file existence check.
Update docs, change markedOptions name, remove temp variables.
Merge in doc updates.
Merge branch 'refs/heads/mattd'

Conflicts:
	README.md
	tasks/markdown.js
Added @mattd and @thomaswelton to the list of contributors
Updated Grunt file so that markdown test works with new files format
Removed htmlExtension and markdownExtension