Create a roll for starting a timer

[omnicolor]

One of the tables I play in uses Raid-Helper, which had a neat feature that I'd like implemented for Commlink's Slack/Discord/IRC integration, a timer.

Users should be able to:

• /roll timer create 15 - to create a timer (in this case for fifteen minutes). /roll timer create 1:00 would create one for one hour.
• /roll timer pause <timer_id> - pause a given timer. If it's a fifteen minute timer and ten minutes have gone by, five minutes would remain when /roll timer resume <timer_id>. If only one timer exists for the channel, the timer_id should be optional.
• /roll timer cancel <timer_id> - stop and remove a timer.
• /roll timer show - show timers in the channel.