reclaim receive buffer space when more than maxFrameSize is free

* Prevents unbounded buffer growth when more than one frame is read
  into the buffer.
* Change buffer to grow by 2x rather than 512 bytes.

Updates #191

add link durability and expiry session to target

Fix Incorrect time calculation for dates before the Unix epoch

AMQP timestamp is a signed value, but decoded from buffer as unsigned.
The previous code took the remainder of the unsigned value before
converting to signed.

Apply connect timeout to Dial

Fix settlement handling and add Message.SendSettled

* Message.SendSettled allows sending messages settled when
  LinkSenderSettle is ModeMixed.

Zero length binary values should not be nil

Clear connect timeout after connection established (#163)

Return server link creation error at time of Sender/Receiver creation.

Server errors during link creation are reported by sending an Attach
without a source or target and immediately sending a follow up Detach.
Check for this situation and wait for the Detach so the error can be
returned to the user immediately.

Fix settlement mode negotiation.

If application has not explicitly requested a settlement mode, any
mode returned by the server is accepted.

If the application has explicitly requested a settlement mode and
the server does not honor it an error is returned during link
attachement.

Fix `shouldSendDisposition()` check in `Message.Release()`