implement the xtrace (-x) and noexec (-n) flags
support for verbose (-v) and parseout (-p)

note: output is done in Plush.Run utilities which is somewhat wrong for doctest and web modes.
add new set flag to doctest
clean up Plush.Run's interface

This simplification was prompted because parsing a command now really does affect execution state.
Notably, the verbose (-v) and parseout (-P) flags can cause output during parsing.
The need to properly handle that output during doctest runs, caused the simplication of the Parse.Run
interface to treat all actions the same, and export a few utility shell actions. The result was simpler
code almost everywhere, and more correct handling of possible errors (including exceptions) during parsing.
shellExec now returns the ExitCode, which simplified some other code