(API Change) Use const params where applicable

This Fixes a minor flaw with the API where data had to always be mutable
to be usable by the API.

Functions that do not modify the fundamental underlying data of a
structure should be marked as constant, both for safety and to signify
that the parameter is input only and will not be modified by the
function using it.

libobs/obs.c

@@ -28,7 +28,7 @@ extern void add_default_module_paths(void);
 extern char *find_libobs_data_file(const char *file);
 
 static inline void make_gs_init_data(struct gs_init_data *gid,
-		struct obs_video_info *ovi)
+		const struct obs_video_info *ovi)
 {
 	memcpy(&gid->window, &ovi->window, sizeof(struct gs_window));
 	gid->cx              = ovi->window_width;