Fixed some issues with authentication related headers parsing/stringification
Fixed some issues with authentication related headers parsing/stringification

'Authorization' and 'Proxy-Authorization' headers are considered multi-values and represented
as arrays in parsed message.

'Authentication-Info' is single valued (there are no 'realm' parameter so there is no reliable way
to distinguish headers from various sources).

voxology/sip-server,kyuucr/sip-websocket,newpouy/sip.js,kirm/sip.js