framework: new hook to only allow 'default' files in category/port

[tcberner]

Summary

This hooks enforces that all files in the top-directory of a port match:

• .*\.mk
• Makefile.*
• dist-info.*
• pkg-descr.*
• pkg-message.*
• pkg-plist.*
• pkg-post.*

An example error message would look like:

[pre-commit] ERROR: invalid file 'Foo' in 'kate/editors'
            Consider moving non-standard files to files/ or force-ignore this hook.

[tcberner]

• fix pkg-* regex (don't enforce presence of a '.' on suffix)

[tcberner]

fix error message "category/port"

[tcberner]

• improve/simplify regex [1]

[1] https://docs.freebsd.org/en/books/porters-handbook/book/#pkg-names

[tcberner]

only check port-category subdirecotries