Fiducials not working correctly #96

The raytracing step for fiducial detection scans as far as the maximum range, therefore fiducials that have an obstacle behind them, in range of the sensor, won't be detected. There's a TODO note in the code reflecting this (line 180 in model_fiducial.cc). Is there some reason the max_range_anon couldn't just be replaced with range, which is the distance to the fiducial?

I tested this and it seems to fix the issue. I'm more than happy to create a pull request if this is all that is needed and it doesn't break anything.