Support exdates and multiple events with the same UID

[jfrumar]

• Factored out the dateParsing so that it can be reused to generate an array of EXDATE directives when they are provided in the ICS feed.
• Index VEVENTs by a GUID since the UIDs provided aren't always unique for each VEVENT. For example, you can create a recurring event in Google calendar, then modify future events based off the master, and they'll all have the same UID - the child events with modifications are distinguished by a RECURRENCE-ID.

[peterbraden]

The tests aren't passing for me - any ideas?

~/repos/ical.js:jfrumar-master$ npm test     

> [email protected] test /Users/peterbraden/repos/ical.js
> ./node_modules/vows/bin/vows ./test/test.js

···································
✗ Errored » callback not fired 
      in with test2.ics (testing ical features) todo item [email protected] 
      in node-ical 
      in test/test.js✗ Errored » 35 honored ∙ 1 errored ∙ 1 dropped

npm ERR! Test failed.  See above for more details.
npm ERR! not ok code 0

[jfrumar]

They are fixed now?