coveralls support

Since the question of coverage was raised I have decided to quickly add a feature... it ended up a sprint  to convince travis and coverage to work as desired...

in the end -- I think it should work:  you can see what it results in e.g. https://github.com/fail2ban/fail2ban where similar to travis status icon is embedded to README and also reports are associated with PRs where tests didn't fail either they increase or decrease coverage

unfortunately there is some glitch with coveralls and my clone at https://coveralls.io/r/yarikoptic/pystatsmodels -- so it reports coverage but while trying to browse files just says Loading... for me (see https://github.com/lemurheavy/coveralls-public/issues/136) but otherwise -- should work.

This is a full protocol of struggle (+ I also reverted tests to be ran without sudo -- that shouldn't be needed, right? + some trailing spaces were removed -- I just needed smth to be pushed ;) )