Adds ordinal direction unit vectors.

[pathunstrom]

Primary use case is to reduce the cognitive load in early lessons:

class OurSprite(Sprite):
    def on_update():
       self.facing = Left

[AstraLuma]

So far, we have not been using ALL_CAPS for constants/flags/etc.

I'm also debating on if we want them available on the root? That kinda gets into making deliberate decisions about what's available from import ppb. (I thought there was an issue for it but i guess not.) I could go either way on ppb.Left vs ppb.directions.Left.

[pathunstrom]

I'll change the casing, figure ppb.directions.Left is probably a good place to start and be open to including it in the core name space if it's requested by teachers?

[AstraLuma]

Good enough explanation.

[AstraLuma]

bors r+

[bors]

Build succeeded:

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