Aha re pandoc, asciidoctor, and asciidoc3

[Edward K. Ream]

Recall that pandoc is a Haskell tool, supporting an enhanced version of markdown. asciidoc3 is a python tool and asciidoctor is a ruby tool.  Both asciidoc3 and asciidoctor support the asciidoc markup language.

Leo can not access asciidoc3 as a python module with any reasonable amount of work. This is a to-do item for asciidoc3, but until that happens using asciidoctor will be faster, and produce better-looking results.  This means that...

Aha: Leo can only access pandoc, asciidoc3 and asciidoctor as external programs. 

Rending in the VR pane

The VR pane will use the following strategy for rending pandoc and asciidoc markup:

1. Use distutils.spawn.find_executable to determine whether the pandoc, asciidoc3 and asciidoctor executables are available.

2. Use asciidoctor (preferred) or asciidoc3 to render asciidoc markup to html. Use pandoc to render pandoc markup to html.

3. Either way, the external tool write the html to an external file. The VR pane will then simply copy that html into the VR text widget.

Summary

It should be straightforward to render either pandoc or asciidoc markup in the VR pane.

I see no reason, at present, to privilege asciidoc3 by having its source code be part of Leo. I'll soon remove the entire leo/extensions/asciidoc3 directory.  I have just closed #1330, for the reasons given here.

Edward