Option to add argument names to function macros in glad.h
I have made a quick modification to GLAD to generate argument names for the macros in `glad.h`, so I can use my IDE to see the GL function signature. Otherwise, I find myself having to look up the documentation for less common GL functions as I'm writing code.

For example, this:

``` c
#define glTexImage2D glad_glTexImage2D
```

Is instead generated as:

``` c
#define glTexImage2D(GLenum_target, GLint_level, GLint_internalformat, GLsizei_width, GLsizei_height, GLint_border, GLenum_format, GLenum_type, const_voidp_pixels) glad_glTexImage2D(GLenum_target, GLint_level, GLint_internalformat, GLsizei_width, GLsizei_height, GLint_border, GLenum_format, GLenum_type, const_voidp_pixels)
```

I'm willing to submit this feature as a pull request if anyone's interested (it works great for me). If so, should I base it on the **master** branch, or **glad2**? I'm new to GitHub so I'm not sure what kind of preferences the project author might have with regard to patches. Thanks!
