Simplify travis testing

Solves #21 by removing tox test and using more simple travis testing.

This test does a flake8 test (L16) which fails at the moment but will pass once the 1021 syntax style violations are solved.

Once pep8 is fixed, the following line would be good to add:
```
install: pip install coveralls flake8 pylint
...
script:
...
    - pylint2 Equation -d R0903,E0611,W0403,E1101
```