New features
Support for the new Kindle Paperwhite 2018.

Closes tickets: 1802088
Metadata plugboards: Allow defining plugboards that modify comments metadata as well.
E-book viewer: Add a keyboard shortcut (Ctrl+M) for toggling between paged and flow mode.

Bug fixes
EPUB Input: Handle invalid EPUB files that have their NCX documents in the spine.

Closes tickets: 1796497
EPUB3 Input: Handle EPUB 3 files that incorrectly use EPUB 2 markup to identify cover images.
Content server: Fix --url-prefix feature not working with book conversion.

New news sources
Arts and Letters Daily by pjpaulpj.
Magyar Idok by pofa.

Improved news sources
Business Standard.
Washington Post.
General Knowledge Today.
How To Geek.