.travis.yml: initial version for travis-ci

This is an initial version of a .travis.yml to build each commit and pull request of embb.
see https://travis-ci.org/bufferoverflow/embb/builds/37236748 as an example.
clang build is currently broken ... feel free to remove it from .travis.yml or fix it ;-)
all the best!
-roger

PS: I've already activated the travis-ci hook on siemens/embb

;-r