automated build on travis-CI

[Anders E.E. Wallin]

I have created an initial travis.yml file and linked the github-repo to travis:

https://travis-ci.org/aewallin/opencamlib

This should build the pure c++ library and the python module automatically.

Any help with better automated builds and testing would be appreciated, e.g.:

- compilers gcc, clang, etc.

- OSs (can we automate mac/win builds?)

- tests and test-coverage (maybe using coveralls?)

- python 2 vs 3 compatibility

- and so on.

Anders