Task: Add sanity tests for PyPI packages before release

[atodorov]

After #133 and #134 we have to add a sanity test/make target to build the packages and compare the contents. Also try to install them inside a virtualenv and report on errors.

While at it also add a sanity check to make sure we're not including any pyc files into the package.

This should run on different Python versions and can utilize
Travis CI build stages so that package build/install tests happen only after all unit tests are PASS.