Changes:
• Chan.I.Messages defines a new well-known header key: "silent".
• Conn.I.IRC_Command1 is now actually marked stable.
• ConnectionManager defines a new well-known parameter: "account-path-suffix".
• Chan.I.SASLAuthentication mechanism X-TELEPATHY-PASSWORD is not mandatory
if unimplementable.
• Tools ported to Python 3.
• Documentation now uses Jinja2 instead of Cheetah for templates.