Allow strings in steps

Two small changes:
- ignore emacs backup files in .gitignore
- added travis configuration to test it (you can configure it for the main repository; mine is here: https://travis-ci.org/magmax/pyspecs)

And a big one:

Instead of using "given.a_new_string", you can use: "given('a new string')". This allows to use spaces instead of underscores, which are more difficult to type in some keyboard languages (like Spanish).

Old format will remain supported.