Removed _|_ as a built in declaration and renamed it to Void

[ahmadsalim]

FalseElim now void to match up.
This is in line with (and concludes) the #1516 renaming effort.

[ahmadsalim]

The choice of renaming FalseElim to void was suggested by @Melvar (thanks!).
I believe it lines up well with the list and either functions that do the same for the (in order) List and Either datatypes.
Perhaps, boolElim should rather be just bool.

[david-christiansen]

Out of curiosity, why not do something like

class Uninhabited a where
  uninhabited : a -> Void
  absurd : a -> b
  absurd x = (elim_for Builtins.Void) (uninhabited x)

instance Uninhabited Void where
  uninhabited = id

This completely avoids needing to name the eliminator, and it shepherds users towards absurd, which IMHO makes easier-to-read programs.

[edwinb]

Is this also updated in the tutorials? I'll merge if so. Once this is done, I'll get a new release together.

[ahmadsalim]

@david-christiansen I actually thought of that, but I was unsure if I should have taken a big semantics altering decision like that, especially since errors are reported differently when type class resolution is performed. So I chose to do a conservative change with only renaming, although I definitely think that absurd is the way to go for most cases.

@edwinb No, not yet. I will get on it soon.

[david-christiansen]

That makes sense. Thanks for doing all this!

[ahmadsalim]

OK, the tutorials are updated now.