v0.14.0 – adds all-stations-M3U, grouping options

[Moonbase59]

• add aggregate M3U per server "<domain>.m3u", allows easier integration
  of ALL stations in programs like Jellyfin, KODI, Hypnotix, etc.
• add --group option; overrides M3U "group-title" from station name
  to something like "Radio-DE", for easier integration into other lists,
  or just keeping your stations together.
• some code cleanup, mainly urljoin(), and more PEP8