Sigil: update to 0.9.13.

Sigil-0.9.13
   Bug Fixes
     - Revert change of INI encoding to utf-8 as QSettings very broken under utf-8 (commit 5484463)
     - Ensure all url attributes in shape-outside properties in CSS stylesheets get updated (commit de7b09f)
     - Workaround for lost cursor in qlineedit Qt bug (issue #398) (commit a8acab7)
     - Workaround missing File New, Open, Quit menus in Mac menubar if windows closed (commit 660a8aa)
     - Remove Icon from Tab for macOS only to workaround Qt bug (commit 5c91924)
     - Plug some memory leaks (commits: 85f78d7, cb9b833, 614d601, bf2f2f4, ebfb613, 4qa8f33)
     - Backport Qt 5.12alpha fix to prevent heap corruption due to qwidget next focus pointers (commit f5c7284)
     - Plug macOS memory leaks when closing a main window (commit fbf9015)
     - Put back quote in tag name bug fix lost in recent changes (commit ebd8c7c)
     - Disable Netscape Plugins being used in BookView and Preview Window (commit 79314ea)
     - Use custom version of qtwebkit with Qt 5.5 memory leak fix added back and no load plugins if disabled
       	   (see commits 94a28d7,  9f7ebba, and 4b968a9)

   New Features
     - Add filename to tab tooltip (commit 27f8db7)
     - Clear memory caches when Preview changes to keep memory footprint smaller (commit 87b9247)
     - Update to MathJax 2.75, adds support for mathml mlongdiv, mstack, mcarries (commit 568aba5)
     - Reduce memory footprint by letting worker threads expire (commit c1ee7ca)
     - Reduce memory footprint by properly setting web page caches (commit 9f07cbe)

Sigil-0.9.12
   Bug Fixes
    - fix typo in cssreformatter that caused errors with @fontface (issue #394)
    - workaround for qt bug affecting tab close buttons on Mac (commit f3b9399)
    - fix Mac Qt5 plugin dylibs that macdeployqt broke in Sigil-0.9.11

Sigil-0.9.11
   Bug Fixes
    - after mend and prettify - put cursor at enclosing tag if possible
    - allow both links in Preview and clicking in Preview to reposition CV
    - fix new cursor repositioning under new tab ala Spellcheck
    - fix prettyprinting of the mark tag in gumbo and sigil_bs4
    - fix crash when tagname illegally (for xhtml) includes single or double quotes
    - fix crash in Reports for non-wellformed xhtml that was okay under html5
    - fix deletion of multiple css files when Book View is open (Windows)
    - fix bug in reformat CSS with media queries
    - fix bug in closing some tabs needlessly when linking stylesheets
    - fix crash bug in gumbo parser under very strange circumstances
    - remove empty guide elements in epub2 opf as epubcheck now flags these
    - fix issue with index generation reordering spine entries under certain conditions

   New Features
    - update official builds to use Qt 5.11.2 and Python 3.7
    - update internal Python modules to use latest versions
    - update Sigil's gumbo parser to fix all known bugs and greatly speedup parsing
    - embed new project css_parser (fork of cssutils)  as a python library to fix css parsing
    - Sigil no longer attempts to upgrade the VC++ runtime on Windows. It only installs the
        bundled VC++ runtime if there is no compatible version already installed
    - add support for internal but unmanifested opf metadata link resources under epub3
    - extend "Open With" context menu to allow up to 5 external editors per resource type
    - make format of all Sigil ini files to be utf-8 encoded to more easily allow user changes

   Changes
    - Support for Windows Vista officially ends ... Win7sp1 is official minimum required Windows
      The unofficial Legacy Windows version of Sigil will be available to XP and Vista users


(wiz)