Modified Makefile to work with Mingw

Applied changes by @imbaczek
Refactor generated code and update to latest glfw-rs

Reduces the size of the binary slightly by reducing and removes the uses of macros. It also brings the loader function up to date with the latest glfw-rs.
Merge pull request #82 from bjz/refactor

Refactor generated code and update to latest glfw-rs
Merge pull request #80 from bvssvni/master

Modified Makefile to work with Mingw