Merge branch 'release/v5.0.0'

Merge branch 'release/v5.0.0'

* release/v5.0.0: (64 commits)
  5.0.0
  Ignore linting demo.css
  Remove links to espeak
  Use HTTPS where possible
  Add links to install additional voices
  Use higher resolution @2x tile in markdown
  Use higher resolution @2x icons in markdown
  Use higher resolution @2x chrome web store banner
  Add Bulgarian translation
  Add language attributes on some untranslated/known language elements
  Translate new strings in the user interface
  Minor translation improvements
  Translate extra variables during static rendering
  Limit number of translated strings per call for google cloud translate
  Switch to using a key file with Google Cloud Translate API
  Speak long text by default in WebExtensions (Firefox)
  Use event listeners
  Fix react popup unload error
  Avoid un/controlled component mixup
  Use reselect to speed up data transformations
  ...