Fix remainder; add splitting by string

[GeorgeLyon]

@wti This actually fixes #22 and adds support for splitting on arbitrary strings.

[wti]

I appreciate the flexibility of String vs. character!

Because implementing (Script) splitInput(...) API seems to require package-internal access to Shwift, I'll maintain a fork wip310plus

[GeorgeLyon]

@wti do you mean internal access to Script? I'm pretty sure all of the Shwift machinery you need is public, but yes as Script is more meant to be a demo for Shwift, and not a dependency in its own right, you won't be able to do things like create new custom builtins.

[wti]

Thanks for the quick replies!

do you mean internal access to Script?

Yes, sorry.

all of the Shwift machinery you need is public

Well, it's Script that has executable's, shell, pipe's, etc. that I and my API clients want to work with.

The goal is a Script (final) pipe sink that operates async per-segment on streaming swift objects (each derived from the segment). Unless the code runs within piping, the memory benefits of processing one segment at a time are lost.

My fork has 3 lines using Script-internal API:

Shell.PipableCommand {
  try await Shell.invoke { _, invocation in
    try await invocation.builtin { channel in

I'll look for alternatives. (No reply necessary.)