Added option to publish max range readings as inf

In the costmap layers there is an option to use max range observations to clear the costmap (using raytracing) - by setting inf_is_valid to true. 

However, this driver publishes max range readings as nan - which makes it impossible to use this driver and clear the costmaps with max range readings. 

Added param to send max range readings as inf.

Set flag no_range_as_inf to true.