Add explicit ranges of dates to the parse_range() method

[zostay]

These changes add a number of improvements to Date::RangeParser::EN:

• Allows for explicit ranges separated by " to ", " thru ", " through ", " - " (I did not implement "between "..." and "... because "between" may imply an exclusive range, which I didn't want to mess with)
• Fixes a couple small warnings about undefined values when a bare month us used
• Gives Date::Manip the same now handling via the now_callback that the Date::RangeParser::EN uses by setting ForceDate
• Changed the way Date::Manip is used so that we try to use the DM6 OO interface when available or the DM5 when needed (or requested)
• Adds a test for the DM5/DM6 bit (which skips if you have Date::Manip 6.00 - 6.13 because DM5 backwards compatibility was added in 6.14)
• Adds more tests for date ranges and some examples of the new ranges
• Documents more formally the kinds of date range terms it understands

I think that's about it.

I adjusted the TODO section of the POD, which imposes some of my own opinions on the project, but feel free to edit my opinions and strike anything you like from the record.

[mjaquilina]

Thanks, Sterling!

This looks awesome at first glance. I'll do some testing tonight and, provided there are no issues, will pull and release to CPAN this evening.