[Review] Request from 'aduffeck' @ 'SUSE/machinery/review_140912_migration_infrastructure'

Please review the following changes:
  * 5973246 Add man page for "machinery upgrade-schema"
  * 704b092 Implement "machinery upgrade-schema" command
  * 9e88640 Require migrations to describe their purpose
  * 410c495 Lazily load migrations from schema/migrations when needed
  * e03d35e Implement the Migration base class
  * a760c31 Extract the JSON loading into a separate method
  * 0797904 Create a SystemDescriptionFactory module for the RSpec tests
  * 7d2c8d4 Add Code Climate badge
  * abd286f Merge pull request #214 from SUSE/validate_existence_of_meta_data_for_extracted_files3
  * f4d5315 Add hint about file meta data validation to man page
  * d08d040 Validate existence of meta data for extracted files