Adding Travis CI to automatically check builds

Current missing are:
- some compilation options that leads to error. They are not corrected
  right now as some of them may by corrected by PR#55
- checkpatch is not downloaded / run because of
  - licenses?
  - CamelCase in GP API that may lead to false alarms

Signed-off-by: Pascal Brand <pascal.brand@st.com>
Minor updates and cleanup