Updated makefiles

Hi, while working on haxe I noticed libs makefiles frequently recompile files when it is not needed. It's not a big deal, since lib updates are rare, but I prefer to use "make" and not "make haxe", so I stumble upon it a lot.
Anyhow, I changed makefiles to recompile only what is needed, and also added a root Makefile, which can be used from haxe Makefile to build everything at once instead of using few lines each for it's own lib.