add signalstats values to decklink capture xml and csv

[dericed]

based off #767.

I'd like a few signalstats values in the xml, such as

<frame n="0" pos="0" pts="00:00:00.000000" tc="01:16:11:01" seqn="F">
   <signalstats satmax="900"/>
</frame>

Note that we'd need to add bitdepth to the <frames> element and to the csv output to contextualize the satmax value.

I'm open minded if these new filter values are as attributes or sub-elements.

[JeromeMartinez]

few signalstats values

Which ones?

[dericed]

So perhaps rather than use signalstats directly we could replicate it by doing our own math. If this is a good direction, let's start with SATMAX, SATHIGH, SATAVG, which is the highest, highest when excluding the top 10%, and the average value of

b=bitdepth
sqrt( (U - 2^(b-1))^2 + (V - 2^(b-1))^2 )