Implement hook system

[mathias-baumann-sociomantic]

To implement https://github.com/sociomantic-tsunami/neptune/issues/48 in an language agnostic way, a generic hook system would be useful

[mathias-baumann-sociomantic]

I can think of four stages for such a hook system

• Begin - Run at the very beginning of the process
• PreReleases - Run before every release, the repo being checked out to the current commit
• PostRelease - Run after every release, repo being checked out right after the tag
• End - Run when all us done, the repo being in the initial branch

[mathias-baumann-sociomantic]

So I am thinking neptune just checks for the directory neptune-hooks/ and runs files matching it's pattern.

The pattern would be

• begin.<name>
• pre.<name>
• post.<name>
• end.<name>

The files are expected to be executable and will be run by bash, so they can contain a shebang line (which means they could even just be d files