Add configuration file Travis CI

After registering at [Travis CI](https://travis-ci.org/), and enabling
the GitHub project in the profile, with this configuration file, every
branch will be build tested, that means, `make` is run.

On GitHub, the branch or merge/pull request will then be annotated, if
the build passed or failed.

This way, simple build errors can be detected before accepting a
merge/pull request.

Currently, the default build environment is Ubuntu 12.04.5 LTS with gcc
(Ubuntu/Linaro 4.6.3-1ubuntu5) 4.6.3.

Signed-off-by: Paul Menzel <paulepanter@users.sourceforge.net>

Author: paulepanter

.travis.yml

@@ -0,0 +1,4 @@
+language: c
+
+script:
+- make