publish: Make publisher more powerful and better exposed on the command line. * Make the `chef publish` command have one sub-command per publish target. * Add custom argument parsing per publisher to have strong extra arguments available per publish target. * Make publish targets a first class citizen of the `PieCrust` app class.

cov-core==1.15.0
coverage==4.0.3
invoke==0.12.2
mock==1.0.1
pytest==2.8.7
pytest-cov==2.2.1
pytest-mock==0.10.1