obs-transitions: Implement fade transition

A basic fade transition that fades to/from a source via a simple cross
fade.

plugins/obs-transitions/obs-transitions.c

@@ -0,0 +1,13 @@
+#include <obs-module.h>
+
+OBS_DECLARE_MODULE()
+
+OBS_MODULE_USE_DEFAULT_LOCALE("obs-transitions", "en-US")
+
+extern struct obs_source_info fade_transition;
+
+bool obs_module_load(void)
+{
+	obs_register_source(&fade_transition);
+	return true;
+}