Mnemosyne 2.11

• Add support for ruby/furigana, i.e '私[わたし]' will render with the
  furigana above the kanji.
• Mnemosyne can now also be installed on top of an existing Python
  installation by doing 'pip install mnemosyne-proj'. This also opens the
  door to an up-to-date install on MacOS.
• Upgrade build system to poetry and test system to Pytest (patch by Ace
  Z. Alba and kuraga).
• Fix more errors in 'Non-latin point size increase' (reported by Hugo
  Coolens).
• Improve icon finding logic (patch by traveller1).
• Fix not remembering last statistics page in some cases (patch by
  Andreas Perstinger).
• Fix rare threading issue in sync server.