option to show url as links without having to use '<' '>' delimiters, using a configurable regex

would be great if we could have a .macdown configuration file where we could customize behavior, eg allowing user to specify a regex to treat something as a link, eg:

.macdown: (either gitconfig like format or json as in sublimetext)
# treat some patterns as links without requiring <> boilerplate

treat_as_link: 'http[s]?://[\w/]+'

Optional extension of this idea:
# treat as file to be opened on a user's computer using user configurable shell command:

treat_as_local_file: '/Users/foo/[\w/]+'
local_file_open_command: 'open'

Start by reviewing the proposed .macdown configuration format and how MacDown currently recognizes links. Define how a configurable treat_as_link regex, local-file pattern, and local_file_open_command should behave, then verify the feature with representative URL and local-path cases.

Written by the indexing model from the issue text.