Refactoring and integrated Travis-CI

* refactored some of the structs to typedefs (could be done more)
* changed some stuff to make it compilable with Ubuntu 12.04 (my environment AND Travis-CI env)
* created Travis yml file with some setup to make it build
* added a README.md with a proud Travis build indicator ;o)

I needed to change your assertions in the hashmap_test.c because the old version of the "check" package in Ubuntu precise does not know them yet.
Also I needed to add -D_GNU_SOURCE to have asprintf() in my environment. Might no longer build in your _BSD_SOURCE environment. We might need a config.h which checks and sets all that stuff depending on the platform.