Support Python: 2.5, 2.6, 2.7, 3.2, 3.3, PyPy. Add Travis CI config

Hello, 

My pull request may looks similar to this one:
https://github.com/galvez/xmlwitch/pull/3

But there are no breaking changes in terms of API.

Also I've added configuration file for Travis CI.

You can check current status here:
https://travis-ci.org/diyan/xmlwitch

If you need anything from me in order to accept this pull request feel free to ask.