This is the first (working) commit that allows iCal attachments for meeting mails. Hence, the mail client can provide a way to easily pop it in the calender.

This requires the standard (http://www.ietf.org/rfc/rfc2445.txt) which is actually accomplished by use of RiCal (see http://ri-cal.rubyforge.org/, http://ri-cal.rubyforge.org/).
The Gemfile is added to deal with this.

The meeting itself has a start_hour and end_hour which is not defined for any time_zone which apperently is very critical for these calender apps - hence the timeZone assumed is that of local.

This has been tested under 2.2.x - with most times being accurate.
The timezone name and date-time-string computation seems to be a little clumsy which I am planning to clean up in next commit.

Any feedback would be welcome.

Dipan Mehta.
A. code clean up - clean methods for event time strings
B. deal with empty date and time strings.
C. iCal generator exception of empty/invalid time is handled - in such case normal mail without invite is sent.
D. changed UID.
E. Added comments.
Adding Gemfile for the new dependency RiCal
Merge pull request #7 from dipanm/master

Add meeting invites functionality as per #5