link support for asciidoc (enhancement)

[boydkelly]

Hi great plugin. I was directed here by https://github.com/kyazdani42/nvim-tree.lua

I notice that some asciidoc links open with xdg-open (on linux), and others don't. Could you include support for:

link:document-b.html#section-b[Section B]
xref:document-b.adoc#section-b[Section B]

see:https://docs.asciidoctor.org/asciidoc/latest/macros/links/

Also how would I change the default opener for a given file type? In fact sometimes I would just want to open the file directly in vim as gf would. But also have the option to open the file with firefox or chrome. It would be nice to not have to fiddle with xdg-open and mime types etc, but just have the plugin get the right opener. It would actually also be very awesome to gx and have the file open both in the current window with vim and a second window for a browser preview.