Viewrendered3 - Better Support For Ascidoc Rendering

[tbp1...@gmail.com]

VR3 version 3.7 brings better support for Asciidoc rendering.  The asciidoctor processor ( a Ruby program) can be used, or one of two Python processors, Asciidoc and Asciidoc3.  Asciidoc in now available as a Pip-installable package (currently V 10.0.2). The new support fixes a bug in Asciidoc.  Math rendering for Asciidoc3 is now working, and math is improved.  If installed, both Asciidoc and Asciidoc3 can be used; a setting lets you choose which one should be used (and the other will be used in case the preferred one is not available).

This version is now in the devel branch of Leo's github repo. A minor update should be available shortly which corrects the Help message information about what delimiters to use for Mathjax math renderings.