vcsh: Make status show commits ahead/behind remote

This is work in progress:
* It does not deal with repos without a remote tracking branch
* It does not share any info if run on a single repo
* I should probably factor this out in a new function

github: in response to richih/vcsh#123
vcsh: Make status() show commit offsets to remote tracking branch

github: Fixes richih/vcsh#123
vcsh: support repo-specific config files
Merge branch 'feature/status_against_remote_tracking'

Conflicts:
	vcsh
Merge branch 'feature/repository_specific_configuration'