libobs: Add level/magnitude/peak volume levels

This replaces the older code which simply queried the max volume level
value for any given audio.

I'm still not 100% sure on if this is how I want to approach the
problem, particularly, whether this should be done in obs_source or in
audio_line, but it can always be moved later if needed.

This uses the calculations by the awesome Bill Hamilton that OBS1 used
for its volume levels.  It calculates the current max (level),
magnitude, and current peak.  This data then can be used to create
awesome volume meter controls later on.

NOTE: Will probably need optimization, does one float at a time right
now.

Also, change some of the naming conventions.  I actually need to change
a lot of the naming conventions in general so that all words are
separated by underscores.  Kind of a bad practice there on my part.

libobs/obs.c

@@ -471,6 +471,8 @@ static const char *obs_signals[] = {
 	"void source_show(ptr source)",
 	"void source_hide(ptr source)",
 	"void source_volume(ptr source, in out float volume)",
+	"void source_volume_level(ptr source, float level, float magnitude, "
+		"float peak)",
 
 	"void channel_change(int channel, in out ptr source, ptr prev_source)",
 	"void master_volume(in out float volume)",