v1.0.0

• throw Preservation::Client::NotFoundError when API returns status 404
• signature_catalog returns Moab::SignatureCatalog or an error when there is no such file; it is up to the caller to handle this as caller sees fit. (part of sunsetting sdr-services-app; the call to get signature_catalog is the last remaining call to be deprecated)
• more streamlined code for handling errors in API calls
• reduce duplication in code for making API calls.
• README updates