completed tests in belief from sensors.

The file used different model for testing. It now used only the unitttest
model as it was intended to.
added a travis.yml file to compile on travis-ci.org.
Merge remote-tracking branch 'thegamebastien/master'
Add function to give elapsed time between 2 measures.

This allow to simulate time or use an extern function to measure
time. This commit also add tests for the new functions.
Refactor code for temporization.

The temporization functions now use the elapsed time versions in order
to reduce the code duplication.
Merge pull request #5 from TACOMA-team/add_projection_functions

Changes in beliefFromSensors