Add terminal markdown

[alvaropinot]

Add terminal markdown support, as proposed here (#4) :)

I just realised that lessmd has no programatic version 😅 but we could use marked-terminal. There will be no pager though 😞.

Here a sample output:

[junosuarez]

I'm good with not having the pager built-in to awesome-npx - people can pipe it to their favorite one. Another option would be to see if the output is the terminal (vs being piped into another process) and, if so, spawn $PAGER as a child process and pipe via that