Show time until next possible update

This uses the git X-RateLimit-Reset header
and displays the ammount of time until the next
possible update using the github api
Suppress timezone warnings if default not set on server

Fixes #13
Merge pull request #23 from addshore/timezoneWarnings

Suppress timezone warnings if default not set on server
Merge pull request #22 from addshore/gitHeaders2

Show time until next possible update