Scan Benchmarks

Following on the discussion in https://github.com/nexB/scancode-toolkit/pull/376 we should have and run scan benchmarks.

@pombredanne commented:

> We should create some benchmarks to watch for any perf changes btw.

@sschuberth commented:
> That would be nice to have indeed, i.e. to have tests to identify performance regressions (or improvements).

>As a first step, looking at the times Travis CI builds take could be useful. Of course, this includes the setup and build times while we're only interested in the time to run tests, and the tests might be too many small projects whereas scanning performance probably is better measured with a single big project, but still.

>So I was quickly giving http://scribu.github.io/travis-stats/#nexB/scancode-toolkit a look, but unfortunately it does not render properly for me. See scribu/travis-stats#12.