Support `min` and `max` builtins

[achidlow]

https://docs.python.org/3/library/functions.html#min and https://docs.python.org/3/library/functions.html#max

key= probably too difficult to support for now.

Inspired by: https://alexandercodes.hashnode.dev/building-a-bitcoin-emulator-on-algorand#heading-difficulty-retargetingadjustment