Viewrendered3 Enhancements

[tbp1...@gmail.com]

A new version of the VR3 plugin has been merged into the devel branch.  The main new features are:

• New command to export generated markup to external editor.
• New setting to specify the external editor.
• Improved readability for RsT parser errors.
  
• Version Change to 3.3.

The new command sends the RestructuredText markup to an external editor.  This is the exact RsT text that VR3 sends to docutils for conversion to HTML.  That way you can examine it, save it to a file so that you can feed it to Sphinx, etc.  The new command is 

vr3-export-rst-html

The data will open in an external editor.  Which editor that will be depends on whether a setting for an external editor has been set.  If not, Leo will use a default editor (e.g., Notepad on Windows).  Any of the settings that change Leo's default editor will work for VR3, or you can use a new VR3-specific setting:

@string vr3-ext-editor = <path-to-editor>

The value should be the path to the editor (without the angle brackets).

The new command and setting are covered briefly in the "About" text.

Please note that this version will not work if you have PyQt6 installed.  After it was released, I discovered that a Qt class, QSvg, isn't available yet.  A new version of VR3 in the near future will work around this, but SVG nodes cannot be rendered until PyQt6 catches up.