Add pager oncall and pager oncall <schedule> commands

[davidcornu]

Removes the who's on call command in favour of pager oncall and pager oncall <schedule>.

Usage:

lita > lita help pager oncall
lita: pager oncall - List available schedules
lita: pager oncall <schedule> - Show who is on call for the given schedule
lita > lita pager oncall
Available schedules: Primary Ops, Secondary Ops, Primary Data, Secondary Data
lita > lita pager oncall Primary Ops
Example User (user@example.com) is currently on call for Primary Ops

[davidcornu]

Fixes #4.

[coveralls]

Coverage decreased (-5.44%) to 93.58% when pulling 77f74f5 on davidcornu:oncall into add887b on PagerDuty:master.

[coveralls]

Coverage decreased (-6.64%) to 92.38% when pulling 0ab2a05 on davidcornu:oncall into add887b on PagerDuty:master.

[coveralls]

Coverage decreased (-6.64%) to 92.38% when pulling 0ab2a05 on davidcornu:oncall into add887b on PagerDuty:master.

[esigler]

Fantastic! Thanks for sending this PR, will look over shortly.

[johntdyer]

Any update here?

[esigler]

LGTM!

[davidcornu]

🎉