Function Kata "Mail Followup"

Implement a function to translate mail followup email addresses into date and time information. See also the Architecture Kata of the same name.

The function to be implemented has the following signature:

DateTime FollowupZeitpunkt(DateTime now, string emailadresse);

Examples for the structure of email addresses:

• 7days@followup.cc
  From now on in 7 days.
• 12hours@followup.cc
  From now on in 12 hours.
• aug15-9am@followup.cc
  Next August 15 at 9 a.m.
• 1week3days5hours@followup.cc
  From now on in one week, three days and five hours.

For example, if the function is called as follows

var t = FollowupTime(new DateTime(2013, 2, 4, 10, 30, 0), "2weeks1day1hour");

then has t the value DateTime(2013, 2, 19, 11, 30, 0).