obs-filters: Add mask/blend filter

This filter allows the ability to use a texture to modify the video
output of a source, the ability to:
- apply a color-based mask (dark = transparent, light = opaque)
- apply a mask based upon the alpha of an image
- blend an image via subtraction, addition, or multiplication

plugins/obs-filters/obs-filters.c

@@ -4,10 +4,12 @@ OBS_DECLARE_MODULE()
 
 OBS_MODULE_USE_DEFAULT_LOCALE("obs-filters", "en-US")
 
+extern struct obs_source_info mask_filter;
 extern struct obs_source_info async_delay_filter;
 
 bool obs_module_load(void)
 {
+	obs_register_source(&mask_filter);
 	obs_register_source(&async_delay_filter);
 	return true;
 }