Listen to all refs on push events (and other small fixes)

[ScottMansfield]

There's three bits to this PR, one of which is more important than the other two:

1. Ability to listen to any ref in a repository. I needed this because I wanted to use a webhook server to sync a remote repo any time any push happened.
2. In verbose mode, print the stderr as well as the stdout of the forked process
3. Small fix to flag code to simplify it and make the -vt flag more symmetric. This is stylistic, so I'd be fine if you don't want it.

As well I created a basic integration test suite to send some sample json through and test the new logic of handling all refs.

[agrison]

Hey @ScottMansfield !

I will of course accept directly 😸

Thank you for your PR, and for the basic integration test that I did not have time to create and forgot since 👍

Cheers!

[ScottMansfield]

It looks like the CI build failed because the TestMain didn't wait for the server to come up before starting the tests. I'll tinker with that a bit.