Enhance CLI usability

[RH-TLagrone]

Enhance the usability of pathschema from the CLI:

• Add a pathschema console script. (required to install via pipx, for example)
• Print schema errors to stderr instead of stdout.
• Differentiate exit codes.
• Add a CLI option to not print anything.
• Add a CLI option to format the results as JSON.
• Add a CLI option to format the result paths as POSIX.
• Add short option names for all CLI options.