Subprocess mode

[DanCardin]

This would enable one to simply kill the current shell to revert state.

Due to lack of any (or at least consistent) support for running shell code on startup of a shell (without screwing with the normal (bashrc, etc) loading sequence, this will likely have to rely on an environment variable.

Potential sequence of events:

• start subprocess with SAUCE_SUBPROCESS=1 env var (automatically +1 from previous/missing value)
• normal sauce shell init bashrc/zshrc/etc loading behavior should cause sauce to be invoked.
• sauce shell init inspects that env var and automatically emits the autoload-hook shell stuff and force-overrides the autoload flag (once)
• that, in turn, causes sauce to execute once, on shell startup

In this way, sauce shell can essentially just start a subprocess in a particular way and the rest should "just work"

sauce config subshell=false/true (default false)

Given subshell=true, sauce shell init would emit a --subprocess flag into the shell invocation (to avoid forcing loading config on a vanilla sauce command.

--subprocess flag would then cause sauce to create a subprocess into the above subprocess workflow would execute.