Fix python-braces format

Python str.format() is marked as `#, python-brace-format` in *.po
(portable object) files.

Add skip_noqa argument to skip "noqa"-commented lines (fix #2)

Add all supported CPython versions to CI suite

- Add CPython 3.5 and 3.6 to travis suite
- Switch travis-ci to container based architecture
- Add travis-ci cache

Refactor `replace_formatters` to use regex substitution to replace
format strings in both C (previously supported) and now Python.

Add support for Python str.__mod__() and str.format() notation.