* Switch cmd/amtool to kingpin
* Touch-ups
* Implement long help
* Add missing short-form of --output
* Fix backwards compatibility for config file options
* Fix vendoring
* Review fixes
* Fix flag word order
* Implement alertmanager cli tool 'amtool'
The primary goal of an alertmanager tool is to provide a cli interface
for the prometheus alertmanager.
My vision for this tool has two parts:
- Silence management (query, add, delete)
- Alert management (query, maybe more in future?)
Resolves: #567