AZW3 Output: When converting EPUB files that include an HTML titlepage no external cover is specified, ensure that the Go to cover action on the Kindle goes to the cover image and not the html titlepage. Fixes #1268657 [Wrong metadata.opf generated for cover in EPUB to AZW3 conversion](https://bugs.launchpad.net/calibre/+bug/1268657)
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Edit book: Add a new tool to automatically arrange all files in the book into folders based on their type. Access it via Tools->arrange into folders.
Documentation for the arrange into folders tool
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Edit book: Add checks for filenames containing URL unsafe characters to the Check Book tool
Move guess_type into the utils module
Allow errors to be associated with multiple locations
Edit book: Add checks for duplicate ids in HTML/OPF/NCX files
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Edit book: When showing HTML tag mismatch errors, show clickable links for the opening as well as the closing tags
Edit book: Add various validity checks for OPF files.

Check for incorrect idrefs, missing required sections, non-linear items
in the spine.
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Check for duplicate items in the manifest
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Check for entries in the manifest that point to missing files
Check for duplicates in the spine
Fix #1269592 [Edit Book: New unreleased Manifest missing files test is buggy](https://bugs.launchpad.net/calibre/+bug/1269592)
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