Some minor (but breaking) suggestions for `categorize()`

1. Current behavior is to return an integer vector. To be consistent with cut(), and to be safer to use, I think this function should return by default a factor - possible an ordered factor.
   • also I think we can drop the lowest argument?
2. The breaks argument in R is usually used to provide the breaking values - here if those are done manually, they are sent to split instead.
3. Rename split to method?
4. 4. We should add a right = TRUE argument, like with cut().

Begin with the categorize() entry point and compare its current arguments and return behavior with R's cut(). The issue proposes several breaking API changes but names no files or tests, so first confirm which suggestions are accepted and where categorize() is tested. Done means the agreed API behavior is implemented and verified without leaving the proposal ambiguous.