Add a !remindme command

[Spud]

Command usage: !remindme in {amount} {unit} {message}

Once the time has elapsed, ping the user with their message

Example:

!remindme in 1 week to go to the csc meeting

... 1 week passes and the bot responds with...

@Spud go to the csc meeting

The amount would be an integer.
The unit would be seconds, minutes, hours, days, weeks, or months.
The message would be whatever the user wanted to be reminded about :P