Convert mailbox and mailbox RW/RO state accessors to properties and
rename to be more explicit about what they mean. Remove mailbox arg
from ::getProtocolState() since it's unused.
Add namespace accessors, handle updating namespaces when processing
the received data, not when executing the command so that unsolicited
namespaces are still recognised. Clear namespaces when new data is
receieved and when not in selected and auth states. Add unit tests.
Move Capabilities to the api directory and make immutable.
Don't pass around out params to simply increment the revision and use a
field in ClientSession, just use the last capability instance. Ensure
after starting a TLS session capabilities are cleared. Add unit tests
for getting both implicit and explicity capaibilities when initiating
a client session.
Allow specifying the connect greeting timeout length, ensure that
any connect errors are in place before releasing the connect waiter,
add unit test to ensure it works properly.
