Add support for Python 3.4

[yasserglez]

I made some changes to support using the package under Python 3.4. The changes rely on the compatibility layer provided by the six package (it was added as a dependency). The examples still use Python 2 syntax, I've only changed pyeasyga/pyeasyga.py and tests/test_pyeasyga.py in order to make the tests pass.

All tests run fine locally under Python 2.7 and 3.4 using tox. It might incidentally support earlier Python 3 versions, but I haven't checked.

I hope it's useful.

[coveralls]

Coverage remained the same at 100.0% when pulling 471970f on yasserglez:py34-support into e155a1f on remiomosowon:develop.

[coveralls]

Coverage remained the same at 100.0% when pulling 471970f on yasserglez:py34-support into e155a1f on remiomosowon:develop.

[coveralls]

Coverage remained the same at 100.0% when pulling 471970f on yasserglez:py34-support into e155a1f on remiomosowon:develop.

[remiomosowon]

Thanks! I have merged your pull request, made some minor updates, and added you to the contributors list. When I have the time, I will test support for the other Python 3 versions and update the repo accordingly. Cheers.

[yasserglez]

Thank you!