Hoon files may want to import nouns from all files in a given directory.
/~ lets you do so, importing as a (map @ta *) (but with typed values).
Note the description as "directories" here, instead of "path prefix".
The behavior, as implemented, will not include /path/hoon for /~ /path,
instead only including /path/more/hoon and more deeply nested files.
This seems to be, generally, the behavior you want, for example when
importing from /app/myapp/* for /app/myapp/hoon.
Actually using the resulting map requires some manual casting, which is
not ideal. Some code style improvement work remains to be done as well.
