Add Travis-CI build file.

Simply ensures the project compiles.
Changed the README file format to Markdown for build image support.

All you have to do if you merge this is go to http://travis-ci.org/ and
log in, then turn on builds for pokemon-online. Also I think travis-ci
will automatically check that any pull requests compile.

You can see that this works at https://travis-ci.org/shancat/pokemon-online/