Rename crate_id to "glfw-rs"

This is so that when the library is installed to `/usr/local`, it doesn't conflict with the actual libglfw library.
Add install/uninstall targets and switch to using a shell script for getting link arguments

Using a shell script should make it easier to include in other projects because it doesn't need to be compiled.
Merge pull request #89 from bjz/install

Improve Makefile with install and uninstall targets