version 1.44.0
Fix regression where multiple coloring rules were used for the same column.
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Merge branch 'master' of https://github.com/cbhaley/calibre

Fixes #1340578 [1.44 breaks column coloring](https://bugs.launchpad.net/calibre/+bug/1340578)
Edit Book: Fix regression that caused crash while syntax highlighting CSS stylesheets that contain url() tokens without enclosing quotes
Fix duplicate entries int he ToC for the EPUB and AZW3 versions of the User Manual
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Edit Book: Fix live link syntax highlighting not being updated correctly after renaming an open file
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