stubbed out the new PGPKeyring and a test harness for it
incremental update to test_reg_bug_56 to begin transitioning into using PGPKey and PGPSignature instead of directly using the packets and TempExportableSig
added stub property __key__ to PGPKey
[skip ci]
Merge commit '723a43f125c66d057a77f552f6925675937315f9' into feature/#80