Editor's drafts for fix-architecture-test-vectors branch of thibmeu/http-message-signatures-directory

Registry and Signature Agent card for Web bot auth	plain text	same as main
Signature-Agent and Max-Crawl-rate for Robot Exclusion Protocol	plain text	same as main
HTTP Message Signatures for Bots	plain text	same as main
HTTP Message Signatures Directory	plain text	same as main