ENH: use logging (with fancy formatter: color, multiline logs indents) + unified run_cmd + minor tune ups

Some kind of clean up must happen before every checkout, since some stale files
might be in place and prevent a checkout.  In general cleaning up .py[co] might be
insufficient if extensions are generated as well

Logging -- coloring is enabled by default unless some of the in/out's doesn't have
a TTY.  Seems to work quite neatly.  By default produces all the output, including
DEBUG, but now much easier to parse.  Also added few more new logging messages.
Timestamping is handy whenever the whole process hangs somewhere and it is desired
to retrospect later on
Merge pull request #30 from yarikoptic/enh/logging_and_running

Enh: logging and running
ENH: moving some functionality from old sample of pandas bench into vbench
ENH: Initiating functionality testing of vbench on a sample small repository
RF: move is_interactive to config -- more logical place
BF: address problems from previous renamings and RFs
BF: copy dependencies after any clean operation -- there is no reason to assume that clean would not clean properly
RF: runner -- make benchmarks a property (compute checksums) allowing their growth + return list of revisions/flags for run() + more logging
ENH: make vb_run_benchmarks.py exit with number of errors so we could warn
ENH: prefix stdout and stderr in logging of run_cmd
ENH: expand functionality test -- should already be useful/usable
RF: Use advised importlib.import_module instead of plain __import__
RF: Move vbench/tests/test-repo into vbench/tests/vbenchtest

having - in a directory which might become a sub-module is not a good idea