Resolve bug in HW3 for loading wrong datatype for image

Refer to [this forum post](http://forums.udacity.com/questions/100126680/hw3-run-local#cs344), original file `loadSaveImage.cpp` has problem -- when it was trying to load image using cv::imread, the image is read as int; while on line 34 it's then referenced as float.

Code added to translate it into float.