Here is a list of all documented files with brief descriptions:

proton
annotations.h
codec.h
condition.h	An endpoint error state.
connection.h	A connection to a remote AMQP peer.
connection_driver.h	Unsettled API - An API for low-level IO integration.
delivery.h	A message transfer.
disposition.h	A delivery state.
error.h	A Proton API error.
event.h	Protocol and transport events.
link.h	A channel for transferring messages.
listener.h	Unsettled API - A listener for incoming connections.
logger.h	Facility for logging messages
message.h	A mutable holder of application content.
messenger.h	Deprecated - Use the Proactor API or Qpid Proton C++.
netaddr.h	Unsettled API - The network address of a proactor transport.
proactor.h	Unsettled API - An API for multithreaded IO.
raw_connection.h
sasl.h	SASL secure transport layer.
session.h	A container of links.
ssl.h	SSL secure transport layer.
terminus.h	A source or target for messages.
tls.h
transport.h	A network channel supporting an AMQP connection.
types.h	AMQP and API data types.
url.h	Deprecated - Use a third-party URL library.