Method decorators support plus some small changes :)

May be it is too much at once.. :) I was too lazy to splitt it in many pull requests..

What is done hier:
* Methods decorators support with first tests for that
* PEP 8 conform,
* maxage renamed to max_age (as you wanted in todo :)
* added tox config and updated travis config for coverage

as syntax sugar also added possibility to bind parameters with function, like
```python
t = Test()
bound_method = t.do_something.bind(param1, param2=4)
assert bound_method.exists()
ttl = bound_method.ttl()
result = bound_method()
```