Setup Travis CI

In addition to the various test scenarios stored in .travis.yml:

- make CLI documentation compiler dependent, using pythran-config
  --compiler new flag
- fix a typo in the DEVGUIDE
- split test_numpy in three parts otherwise travis times out. It was too
  big anyway
- fix libs flags
- remove test_simd as travis does the job for us
Fix numpy's version of power operator
Fix double free
Fix PythranExtension compiler

Make sure to use the compiler from .pythranrc if available.
Merge pull request #313 from serge-sans-paille/travis-ci

Travis ci