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Update source code links
Edit Book: Fix individual find and replace not working in regex mode if the search expression uses lookbehind/lookahead operators
calibredb list: Fix error if one of the requested fields if empty for all requested books
Fix #1276127 [calibre/src/unrar/unpack.cpp:1159]: (style) Array index 'CurBitLength' is used before limits check.](https://bugs.launchpad.net/calibre/+bug/1276127)
Fix tag highlighting breaking when a line is edited because of stale user data
Edit Book: Shortcut change of current paragraph to heading

Edit Book: Add a tool to easily change the current paragraph (the
paragraph containing the cursor) to a heading. Simply click the button
with 'H1' on it and choose the heading level you want the current
paragraph changed to.
Linux installer: Install appdata files for integration with software stores. See #1271974 (Please include an AppData file)
calibredb add_custom_column: Fix a harmless error message when adding custom columns caused by the new db backend
pep8
PDF Output: Fix a zero division error when the transformation matrix has a zero diagonal
pep8
Edit Book: When running Replace All add a button to the replaced message to show exactly what changes were done
Fix button ordering
Compare books: Fix incorrect scrolling when viewing all text and a large amount of text is present after the final change.
Compare books: Fix non-optimal display of changes in some situations

Extra changes were being displayed because the patience diff algorithm
can return large replace blocks with identical leading lines. Instead of
showing them as diffs, show them as extra context.
Adding books: Implement a copy to clipboard button for when duplicates are found during the adding process. Useful if you wish to review the list of duplicates later. See #1276918 (The Popup for duplicate records does not have a "copy to clipboard" option that would be most useful)
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Edit Book: Fix another bug in the save/close/re-open edit cycle for AZW3 that could cause images/fonts to get mixed up. Fixes #1276726 [Private bug](https://bugs.launchpad.net/calibre/+bug/1276726)
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