Log Message:
Sigil: update to 1.9.20.

Sigil-1.9.20
    Bug Fixes
      - double width of new Find Replace icons to make them easier to access
      - improve new Find Replace icon tooltips to be include short name on top
      - fix bug that caused file rename changes to fail when updating smil
      - Metadata Editor will now strip out unneeded xmlns:dc attributes on dc tags
      - Metadata Editor is now more robust to language codes that have incorrect \ 
case in the metadata
      - clarify Create HTML ToC menu entry works from existing ToC
      - prevent indavertent "\" chars be treated like escapes when \ 
updating metadata
      - fix MetaEditor nit of not auto adding "aut" role to Author \ 
metadata for epub2
      - make Spellcheck Editor count align column numerically (right)

     New Features
      - add ability for a user-template*.xhtml and user-template*.css
          be read from Sigil Prefs to create new empty xhtml and css files
      - updated to very latest MathJax version 3.2.2 for mathml support in Preview
      - add ability to cycle through 2 different custom stylesheets (and none at \ 
all) for use with Preview