Transition payload hash option names to hmac

The payload-hash-* options are imprecisely named. Clarify their function
as HMAC validations by renaming them. The existing options will continue
to work but are deprecated.  Log a warning if the old options are used.

All tests, examples, and documentation are updated.

Fixes #289

hooks.json.example

@@ -33,7 +33,7 @@
         {
           "match":
           {
-            "type": "payload-hash-sha1",
+            "type": "payload-hmac-sha1",
             "secret": "mysecret",
             "parameter":
             {