- added: new utility api sensor
- added: basic scanning functionality
    method scan(enter_callback, leave_callback) can be used to react to
    players entering/leaving the sensor range providing callback methods and
    returns a list of all players currently in sensor range
- modified: added checks for callback functions in scan()
Merge branch 'sensor_api' into dev
- added: new utility visitlog
- added: basic logging functionality
    a log gets created and written to everytime a player enters or leaves
    the sensor range
Merge branch 'visitlog' into dev