#419 - Fixed Illegal characters in path

Regex for getting the markdown link for AssociatedImages was also
pulling in the optional title. Since the optional title includes a "
character it was causing Path.IsPathRooted to fail. Updated the link
word boundary to exclude the optional title if present.
#419 - Added unit test for optional title fix

Added a unit test that includes an image with an optional title defined
as well as an image without.
Merge pull request #428 from myquay/master

#419 - Fixed Illegal characters in path