Create empty texture idea, change function scopes

Some functions which should not be exposed in the API have been switched
to INTERNAL scope. We have a notion of an empty texture in World Traveller
that we can pass in situations where we just want to render a solid
colour with no associated texture.

The alternative to this was creating a separate shader for rendering
primitives but would require at some point to expose the AssetManager to
the renderer or the user on behalf has to manually switch shaders before
rendering (non-intuitive).

src/Texture.c

@@ -28,8 +28,8 @@ INTERNAL GLint getGLFormat(i32 bytesPerPixel, b32 srgb)
 	}
 }
 
-Texture genTexture(const GLuint width, const GLuint height,
-                   const GLint bytesPerPixel, const u8 *const image)
+Texture texture_gen(const GLuint width, const GLuint height,
+                    const GLint bytesPerPixel, const u8 *const image)
 {
 	// TODO(doyle): Let us set the parameters gl params as well
 	glCheckError();