Make STATIC_DIR an argument and get rid of `test_paths` feature

[nickfarrow]

I think by default we should use

STATIC_DIR = "static";

And give people the option of setting it using a config argument if they want to host nolooking from a more exotic directory.

Then could we get rid of the test_paths feature, instead passing it as an argument with the tests?

[Kixunil]

I think there should be some build-time option to use a specific default directory so people using packaged version don't need to override it. But maybe it's best to just set default in config_spec.toml and patch it during packaging. Maybe this is something configure_me should support better.