Bloated Build system

Currently, the SDLU build system is heavily bloated, containing support for CMake, premake, GNU autotools as well as a pre-created makefile. This may be just be too much given that the library is not actually that large to require such a complex build system.

The new build system will most likely be CMake (configure may be kept, because, eh, I put much work into it in order to just throw it away), with proper documentation so as not to confuse new-comers.