Cmake rewrite

I've been working on a Gentoo ebuild for GLCS, and ran across a few hiccups in the cmake build system, so I rewrote it. Here's the list of stuff changed in this branch. :smile:

 * Automatically generates the GLC version number using `git describe`. Falls back to GLC_VER if not building from git, or the user doesn't have git. (see below)
 * Removed hard-coded search directories from find modules, so packagers can override them. (for building 32/64 bit versions, for example)
 * Added the ability to build against a system-installed version of glcs-packetstream, which does not install optimizations.h.
 * Added a `.gitignore` file that ignores generated files in case someone uses cmake in the source directory.
 * Added LIBRARY_INSTALL_DIR as a synonym for MLIBDIR.
 * Removed the header file installation target. (see below)
 * Put quotes around strings.
 * Fixed indent inconsistency.
 * Other general formatting consistency changes.

Right now, the version string generated by `git describe` is just the commit ID. If you make a git tag on a release commit, the version number will be something like "0.6.2" for the unmodified release, or "0.6.2+3-cf24fa" for development builds. Much easier than that weird `gen_version.c` thing. :wink:

I didn't see a reason why a user would need the header files installed system-wide, so I removed the header installation target, but I can put it back in no problem, if it's important.