Fixed PEP8 issues
Configured first testing setup

- Tests are run using pytest
- Test environments are set up using tox
- Right now, Travis-CI is set up using a Qemu installation, in which
  tox is run
- Coverage is measured
- Coding guidelines are enforced
Added coveralls configuration
Merge pull request #19 from py3minepi/pytest

Introduce Pytest, Tox, Coverage