Amended ISO8601 date formatter

[patricklodder]

Implements full ISO8601 Date support.

Changes:

• Decoding will now always take UTC offset into account (previously it was ignored)
• Decoding now allows timestamps without colons
• Decoding allows timestamps without minutes and seconds
• The date encoder gained several config options:
  • Using hyphens between date fields (default: off)
  • Using colons between time fields (default: on)
  • Encoding to UTC instead of local time (default: local)
  • Appending UTC offset to local time (default: off)
  • Appending milliseconds (default: off)
• Default encoder config is currently set to provide 100% backward compatibility
• The DateFormatter instance is exposed as xmlrpc.dateFormatter, to allow for formatting option changes in implementations (see the updated README.md)
• New unit tests for the date formatter under test/date_formatter.js

[baalexander]

Thanks @patricklodder for the DateFormatter improvements and adding the unit tests!