Overhaul CLI

[Aloso]

Is your feature request related to a problem? Please describe.

The CLI interface is cumbersome to work with:

• The --test <ENGINE> is weird. It is unexpected that it takes an argument, and the engine (which would be more intuitive as an --engine argument) might be needed for other commands as well

Describe the solution you'd like

I realized that we can add subcommands backwards-compatibly (as long as their names are no valid Pomsky expressions, so pomsky test is fine).

We add a test subcommand and deprecate the --test flag. The engine is specified with the --engine/-e argument instead.

The --path argument accepts a directory when in the test subcommand. Ideally, all Pomsky files can be compiled and tested with a simple invocation:

pomsky test -e pcre2     # assumes --path .

Note that the flavor or the engine needs to be specified. It's not great to have PCRE as the default flavor for testing.

Other possible subcommands are:

• pomsky check - analogous to pomsky test, but it only compiles, without running tests
• pomsky eval - compile and test a regular expression in a REPL. pomsky eval --regex can be used as regex-test replacement.

[Aloso]

The test command is working (including directory support), but the code needs a lot of cleanup.