Log Message:
Updated calibre to 2.83.0.

- version: 2.83.0
  date: 2017-04-15

  new features:
    - title: "PDF Output: Default to generating PDFs with a page size of \ 
letter instead of taking the page size from the output profile."
      description: 'This avoids user confusion/bug reports about PDF Output \ 
having "too large fonts". There is a new option "Use profile \ 
size" to have the conversion use the output profile page size instead.'

    - title: "PDF/DOCX Output: Add separate, pdf/docx specific, page margin \ 
settings that override the common settings."
      description: "Useful because page margin settings for page oriented \ 
formats, such as PDF and DOCX are usually different than those for reflowable \ 
formats such as EPUB"

    - title: "Table of Contents tool: Add an undo button"

    - title: "Metadata jacket: Show custom rating columns using stars"

    - title: "Metadata jacket: Change formatting of series to match that \ 
used by the book details panel. Also allow access to the raw series name and \ 
number when customizing the jacket template."

    - title: "calibredb check_library: Vacuum database when running the \ 
check"

    - title: "Check Book: Add a check for empty identifier elements"

  bug fixes:
    - title: "Edit book/Book polishing: When adding a cover to an EPUB 3.0 \ 
file set the svg property if a SVG cover wrapper is used"

    - title: "Refresh the book list when a User Category is added/edited."

    - title: "EPUB metadata: Fix deleting ISBN from EPUB file could result \ 
in an EPUB file without a package identifier if the ISBN was used as the package \ 
identifier."

    - title: "Amazon metadata download: Fix title and author names being \ 
bold in the downloaded comments when using bing to get amazon metadata."

    - title: "PDF Output: Fix a regression that broke PDF Output for \ 
documents containing mathematics."

    - title: 'E-book viewer: Fix a regression that broke the "Clear \ 
recently read books" action in the viewer'

  improved recipes:
    - Go Comics
    - Die Zeit (subscription)
    - Pagina12
    - New York Magazine

  new recipes:
    - title: Jacobin magazine
      author: Darko Miletic