Generalized date regexes

First off, I wanted to thank you for writing and releasing this plugin - it is just what my small startup needed.  My colleague Matt Ewing was corresponding with you for help on getting it working for us.  I finally had a chance to dig in and I figured out the reason - it was designed to work for events that have start and stop hours, and we were using whole day events, which have a different format in the ICS file.  I modified your regexes to work with either format, wanted to see if you'd be inclined to add the changes to the main branch of the plugin. As you can see, the changes are fairly small.

Best,
Dan