Change tundra.tn:deliver to include username and redacted password
in logged URL to provide evidence of the authority used; closes #42
Change tundra.tn:receive to redact the Authorization header for
HTTP requests when adding the transport info content part; also
change the format of the content part from XML to YAML so it is
smaller and easier to read; closes #41
Change tundra.tn.document.content:add to use the following precedence
rules for determining the encoding of the content:
1. Use $encoding if specified
2. Use $content.type charset parameter if specified
3. Use UTF-8
Add tundra.tn.document.attribute.string.transformer.user:current
for extracting the currently logged on username as a bizdoc attribute;
closes #43