Bulk for review:  initial support of benchmarking multiple branches, simple regressions report

Hi Wes,

Sorry for keeping it on the private shelf for too long -- now it is a bit too much of changes at once, but hopefully you would get a moment to review at least commit msgs for general feedback.

Multiple branches support is not yet fully cooked and I haven't finished testing yet on a real repository (running now for numpy), but I will get back if it worked fine -- so probably do not merge as is this PR for now ;) 

As for without multiple branches support -- you can see result on running NumPy vbenchmarks: 

http://www.onerussian.com/tmp/numpy-vbench/

Cheers