[pivyjldt] Command line arguments as a tree

Provide a means by which command line arguments are given and always interpreted as a tree (a forest), not a list of strings.

Should the parser go in the shell, or the program? The latter allows incremental deployment alongside already existing programs.   The former allows a completely new method of invoking programs, with opportunities for a new shell to preparse and reuse saved trees.

Obviously inspired by a Lisp shell.

For backticks to work, we might also want a means for standard output to always be a tree instead of a string. This is a profound change. Mathematica does this inside of its walled garden.