Add option to show pv length like 5 plies

[fsmosca]

If there is mate score, show all pv moves, if not just show 5 plies.

It is odd number so I can analyze, like:
mymove, yourmove, mymove, yourmove, mymove -- then see the eval.

[jhonnold]

mymove, yourmove, mymove, yourmove, mymove -- then see the eval.

Is this currently not possible with the long PV?

If there is mate score

Tom's Live Chess Server (the broadcasting tool Graham uses) doesn't send mate scores, but the number it does send is so unique I can probably just use that to trigger a full PV.

[jhonnold]

Unsure what this means still.