release 5.13

• removed Python 3.6 from the support list (it is EOL). Now supported on Python 3.7 or newer
• corrected documentation about autoproxy: this feature is not configurable, it is always active.
• introduced SERPENT_BYTES_REPR config item (and updated serpent library version requirement for this)
• flush nameserver output to console before entering request loop
• added optional boolean "weak" parameter to Daemon.register(), to register a weak reference to the server object
  that will be unregistered automatically when the server object gets deleted.
• switched from travis to using github actions for CI builds and tests