Add better main

[jamesaorson]

Introduce an optional main which provides the environment of the program parsed out and ready

type DayArgData struct is
  data: ptr<ccstring>
  length: size_t
end

type DayEnv struct is
  args: DayArgData
end

fun day (env: DayEnv) int do
  ? do work...
  0
end

[jamesaorson]

Rather than write a new main, a system will be written and designed to plug in multiple mains which are executed via different CLI args from the user.

This system can then be used to create some starter improved mains added to the standard library.