add hash support.

I would like to add hash support to the process object.
This can be done a few ways, I am sure. In this commit, I just copied the implementation from the File Object into the process object.

Another option would be to replace 

 image_info = cybox.TypedField("Image_Info", ImageInfo)

with
 image_info = cybox.TypedField("Image_Info", File)

I realize that this might have to be discussed prior to being accepted. Let me know if I can help and or answer any questions.

Thanks!