Support for clearing the cone if on max reading

This change is to add a parameter that allows for the clearing of all elements in the sensor cone in the event of a range reading above the max value in the range message.  In doing so, the map can keep clear of ghost obstacles in the case where a sensor reading is given above max range for no detected obstacles within range.  This behavior matches better with the semantics of a reading above max range.  It is an additional parameter for the layer though, in case this behavior isn't present in the sensor providing the range messages.
Support for clearing the cone if on max reading

This change is to add a parameter that allows for the clearing of all elements in the sensor cone in the event of a range reading above the max value in the range message.  In doing so, the map can keep clear of ghost obstacles in the case where a sensor reading is given above max range for no detected obstacles within range.  This behavior matches better with the semantics of a reading above max range.  It is an additional parameter for the layer though, in case this behavior isn't present in the sensor providing the range messages.
Limit the clearing on max reading

Only clear to the range which is known to be safe (i.e. max_range).
Merge pull request #8 from MattDerry/hydro

Hydro