fixed calculation of furthest_scan_position; fixed implementation of Reader.__getitem__ according to python Data model; added comments
fixed calculation of furthest_scan_position; fixed implementation of Reader.__getitem__ according to python Data model; added comments

BerlinUnited/NaoTH,BerlinUnited/NaoTH,BerlinUnited/NaoTH,BerlinUnited/NaoTH,BerlinUnited/NaoTH,BerlinUnited/NaoTH,BerlinUnited/NaoTH