Cannot pass GLRepeat to glTexParameteri without manually casting to cint before
* **What is the current behaviour?**
Failure to compile, when writing:
```nim
glTexParameteri(GLTexture2D, GLTextureWrapS, GLRepeat)  <------ GLRepeat is GLenum, not GLint
```
```nim
# From nimgl/opengl
GL_REPEAT* = 0x2901.GLenum
proc glTexParameteri*(target: GLenum, pname: GLenum, param: GLint): void {.stdcall, importc.}
glTexParameteri*: proc(target: GLenum, pname: GLenum, param: GLint): void {.stdcall.}
```
```nim
# Solved manually with:
glTexParameteri(GLTexture2D, GLTextureWrapS, GLRepeat.cint)
```
* **Please provide the steps to reproduce and if possible a minimal demo of the problem**
As above

* **What is the expected behaviour?**
Being able to pass `GLRepeat` to `glTexParameteri`, without having to manually cast it to cint

* **Please tell us about your environment**
  - NimGL Version: [ 1.3.2 ]
  - OS: [ Linux ]
  - Bindings: [ OpenGL ]
  - Backend: [ C ]
  - Nim Version: [ 1.7.1 ]
  - Compiler used: [ GCC ]

* **Other information** 
_(e.g. detailed explanation, stacktraces, related issues, suggestions how to fix, links for us to have context, eg. stackoverflow, docs.gl, documentation etc)_  
Not sure what else is needed. I think the case is fairly clear with that code, but let me know if I'm missing something important.