Merge branch 'master' of https://github.com/cbhaley/calibre
Fix importing of C-extensions when people are running from source with a PYTHONPATH containing conflicting pre-imported modules
Driver for Onyx T68. Fixes #1336868 [Detection debug Information for Onyx T68](https://bugs.launchpad.net/calibre/+bug/1336868)
Dark Reading by Brandon Allberry

Fixes #1337388 [Dark Reading recipe](https://bugs.launchpad.net/calibre/+bug/1337388)
Add a wizard for easily searching date fields in your library. To use it click the advanced search button to the left of the search field. Allows you to search for books whose date is older/newer than a specified date or less than a number of days ago and so on.
version 1.43.0
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Start work on API documentation for the new database API
More API documentation
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API documentation for the Container class
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Move all China related recipes into a single category

Fixes #1338001 [Change in categorization of news sources](https://bugs.launchpad.net/calibre/+bug/1338001)
More API documentation
When calculating the recommended folder for files of a given type, if no such files already exist in the book, use the folder containing the OPF file rather than the root
Book polishing: When changing the cover in an EPUB file, place the newly created cover image in the same folder as other images in the book, rather than the root
Finish API documentation for the container and associated tools
Refactor for reuse
Improve performance of column coloring:
1) cache the results of calling the formatter even if they are negative.
2) use compiled templates