Pixels per meter update

Here are three unrelated commits I'm putting together in this pull request. The real important one is the pixelsPerMeter update.

The use-case I have is a top-down sport game where the arena's meter size is proportional to the number of players, and this requires pixelsPerMeter to behave properly when updated in the middle of a scene.
Yes good point, I updated it.

I would prefer to keep the connection logic simple, even though those are very edgy cases.