Add specification and the implementation for a basic coverage statement
CoverageStatements don't need the item's collection at this point since Primo collapses all collections for a given sub library down into one availlibrary element
Add failing specs for the coverage statement in NyuAleph
Come correct with the semantics of the spec
Update the Primo config to correctly handle the Primo library to Aleph sub library mappings
Update coverage statements to work
Implement coverage with CoverageStatement objects
Merge pull request #12 from NYULibraries/feature/coverage_statements

Refactor coverage statements. This is just a start and can definitely be improved upon.