Added resize parameters for dataset image reader, and the ability to loa...

...d data from alternate directories

cc @eickenberg 

Added the ability to specify arbitrary directories for the load_sample_images and load_sample_image functions to enable loading "other data" easily. 
I think this would be nice - the only thing I don't know is what images PIL supports. I thought it was only jpg but I may be wrong. If it supports more than jpg I am 100% ok with opening up the glob as well.