New features:
  - Added support for Python 3.0+
  - Added support for Neovim Python
  - User autocmd triggered when plugin is loaded on-demand
  - Shallow clone by default

Improvements:
  - Updated for the new Neovim job control API
  - PlugUpgrade using git
  - Ignore case for "<Plug>"

Bug fixes and others:
  - Fixed &rtp missing on-demand loaded plugins when .vimrc is reloaded
  - Temporarily change &shellredir
  - Force evaluation of &statusline before running the installer
  - Explicitly specify format for `git show`
  - Fixed local plugin judgement on Windows
  - Changed the default number of threads on Windows to 1

Acknowledgements:
  - @starcraftman
  - @vheon
  - @itspriddle
  - @mhinz
  - @hori-ryota
