Update to 2.21:
- Make sure that file is regular file when getting local hash
- Fixed crash in Downloader::checkStatus
- Ignore extras without filename
  These are usually extras that haven't been released yet so they
  can't be downloaded anyway
- Changed jsoncpp include path from <jsoncpp/json/json.h> to
  <json/json.h>
- Added support for saving serial keys
  Serials are saved to "serials.txt" when using --save-serials with
  --download and listed in the output when used with --list-details
- Show more info on HTTP error in API::getResponse when using debug
  build
- Added option to skip fast platform detection
  --no-platform-detection skips the initial fast platform detection
  and detects the supported platforms from game details which is
  slower but more accurate.
  Useful in case platform identifier is missing for some games in
  the game shelf.
- Fixed downloader skipping some files because of uncleared API
  error state
- Show url in http error messages

(wiz)