Added basic comments to files. DRY on ContractDecorator. Added augmented...

..._design pdf.
@isupeene Added basic comments. Please review especially parallel_merge and parallel_block_exchange comments. 
Removed ContractDecorator module for DRY.
Added pdf of augmented design doc located at https://docs.google.com/a/ualberta.ca/document/d/1bvc2GpNBwODDFmKvfB91gpsVKCiouT-7_jlT_YmFLoU/edit
Please tell me if you change that doc so I can make a new pdf.
Exchanges the block of elements in the slice below `start_upper` with the block of elements at and above `start_upper`.