Work towards feature parity with Gophernicus' gophermap format

[dotcomboom]

gopher://rawtext.club/0/docs/gophernicus/README.Gophermap

Namely..

# Hide a few files from the menu listing generated by *
-hiddenfile.txt
-hiddendir

# Change filetypes for this directory
:png=g
:foo=b

Additional type characters supported by Gophernicus:
   #          comment - rest of the line is ignored
   !title     menu title (use on the first line)
   -file      hide file from listings
   :ext=type  change filetype (for this directory only)
   ~          include a list of users with valid ~/public_gopher
   %          include a list of available virtual hosts
   =mapfile   include or execute other gophermap
   *          stop processing gophermap, include file listing
   .          stop processing gophermap (default)

I imagine ! functions like a Gophertag.
Of type characters that will most likely be left out: ~, %, .. (* is a glob, those are already implemented). (Executable Gophermaps will most likely be left out for security reasons; an alt handler could be used instead.)