Initial implementation of verify-consistency.rb

Added the .rb extension to both files (since they rely upon being
in the same directory as marlin.rb anyway). Implemented initial
version of verify-consistency.
Finish up verify_consistency

Roughly implemented the rest of verify_consistency
Refine verify-consistency.rb

Corrected a few syntax errors and semantic errors.
Add README, finish implementing verification of consistency

Finished implementing the core portion of consistency verification
(i.e., ensuring all of the entries have the same size and hash). Added
a README.