Continuous Integration

I've succesfully set up a Travis-CI with some details that I will share here.

First, the versions tested are:
 - Python 2.7 and Python 3.3
 - NumPy 1.6.2, 1.7.1 and 1.8.0. Basically the last bugfix version of the three last minor versions. Ubuntu 12.04 LTS has NumPy 1.6.1 but I tested against NumPy 1.6.2 because is in Debian stable. It's very easy change the version in the `.travis.yml` file.
 - SciPy 0.13 (latest stable release)
 - matplotlib 1.3.1 (latest stable release)

Then, all are combined in different environments except NumPy 1.6.2 and Python 3.3 because NumPy 1.6.x does not support Python 3.3.

I've renamed (temporally at least) some test files in order to set up easily the tests with `pytest`. This could change when a standard arrives.

I patched paths to data but this only works launching all test from the root directory.

With the current configuration (considering absolute imports) is not possible testing the package without install it. This is a defect and should be corrected.

`setup.py` now uses `find_packages()`.

Also, I fixed some small errors in tests. One was a typo and other was a "print incompatibility".

All tests have passed in Travis. The log files have more than 10.000 lines so it would be good trying to run some installations (numpy, scipy, matplotlib and other) less verbose, to see in the UI how the build finished.

Before merge, please read the ["Getting started"](http://about.travis-ci.org/docs/user/getting-started/) for Travis. You should follow steps 1, 2 and 4 to enable builds from the main repo. There is a lot of information about how to write the configuration file that you can skip it if you like.