Optimize some PIsList utilities - add a few more utilities

[TotallyNotChase]

• Add some missing phoistAcyclics to top level utilities.

• Remove redundant plet usage from plength.

• Make plistEquals manually go through both lists at once (using pelimList). This should be significantly more efficient than zipWith followed by foldr.

  It looks like the entire result of zipWith is evaluated before foldr is called.

• Make pall use precList directly.

• Add pany.

• Add pfoldrLazy. This takes in a (a :--> PDelayed b :--> b), rather than (a :--> b :--> b) - allowing the fold to short circuit.

• Add left folds, pfoldl and pfoldl'.

• Add some tests for pfoldl.

Closes #79

[L-as]

Can we put this into staging to reduce merge conflicts later on?

[L-as]

LGTM

[L-as]

If only we were using Pijul.

[TotallyNotChase]

Can we put this into staging to reduce merge conflicts later on?

Done!