This enhancement offer the possibility to open articles in the background by using the browser hotkey Ctrl+Return or Cmd+Return.

This better matches the most common use case for the "Mark this page as
read" link, which is to click it once you have reached the bottom of the
page. Especially on mobile, it can be annoying to scroll to the top of
the page to click the link.

See this workaround: https://stackoverflow.com/questions/32639694/ios-9-removed-the-possibility-to-change-certain-symbol-colors-using-css/38362138#38362138

- Add more links to the docs
- Add screenshots

Only for feeds that reach `maxParsingError` are counted (so transient errors do not trigger counter).

Addresses #205

Changed error level reporting on API login failure to Error from Info to match the web login reporting.

Fixes #205