v3.0.6

Changes from @pirtoo.

• Pull common Plex requests into a function with more error reporting on failures.
  • Reuses code.
  • Provides errors on server failures or forbidden when plex token is wrong.
  • raise SystemExit if a request fails without an exception rather than carrying on.
  • Use requests module's ok definition and status_code/reason for errors without outputting HTML.
    Fetch a second playlist if there is one to extend detection
• If (like on my system) the first playlist happens to be all one artist prefix detection fails. Try two if there is more than one playlist.
• Add an indent to pretty-print the variables.json file when it is output to make it more human readable/editable after the fact.
• Give more detail on reasons loading an existing variables.json file may have failed.
• Exit when failing to read existing variables.json file.
• Switch quoting on one line to not need to escape single quotes and remove unneeded escaping.
• Detect and give a more visible warning before exit when updating plex playlists fails (such as when the directory isn't readable by plex).
• Update example variables file to current variable names.