Add static generator

Close #163
The same code is already in the other two generators, I added it here: https://github.com/bjz/gl-rs/commit/e6af4518150c0997301b1d031a2517499e00836d

The reason why it's there is because there are some hacks in the official specs.
In the GLX specs, there is a GLenum whose value is `"GLX"` (yes, with the quotes).
In the EGL specs, there are several GLenum whose values are `(Type)value` (for example `(EGLContext)0` or `(EGLint)-1`)

This code is here to filter that. If the value of the enum is like `(Type)value` (that's what the regex is for), then the type and the value of the enums are changed to the right values.