Beef up the build system and add build docs

Getting the vanilla makefile to work on Fedora was a PITA as I had to manually resolve all the dependencies, and, moreover, pkg-config is a bit broken on Fedora when both 64bit and 32bit libraries exist side by side.

So here's a `CMakeLists.txt` to replace the Makefile that

1. checks whether required 32-bit dependencies are installed, and
2. robustly handles the compiler and linker flags

Since CMake is required to build dfhack, which many DF players user, it is my assumption it isn't an unnecessary dependency to add.

I also added the required dev packages for Fedora 20 to the README, presumably other distros could be added as well.