administrative changes

Before making any edits to the specification I wanted to simplify the build process a bit:

* switched the makefile over to use [xml2rfc](https://pypi.python.org/pypi/xml2rfc/)
* updated the README.md with a bit of information about what the repo is for and how to get started
* added [travis-ci](http://travis-ci.org) support so that pushes to Github trigger a make which will report invalid xml, etc.

If you need help getting travis-ci setup let me know. You basically just login to travis-ci.org and then turn on your bagitspec repository. When you do it you'll want to s/edsu/jkunze/ the links at the top of the README.md.