Miniconda based Travis-CI configuration

Travis-CI configuration uses miniconda to build a suitable test environment.  Benefits to this approach include:

* install binary libraries/modules from binstar
* run all the unit tests
* add support for testing against Python 2.6 (and in the future 3.3)

This also add the necessary hooks to add unit test coverage information to Coveralls.io, which will show up at https://coveralls.io/r/ARM-DOE/pyart once merged and the CI has run.  As an example look at the coverage report for the [jjhelmus fork](https://coveralls.io/r/jjhelmus/pyart)