v0.12.5: 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

v0.12.4

add link durability and expiry session to target

v0.12.3: 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.

v0.12.2

Apply connect timeout to Dial

v0.12.1: Fix settlement handling and add Message.SendSettled

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

v0.12.0

• Additional validation of received messages. Bumping to v0.12 as additional validation has the potential to cause issues with non-conforming brokers.
• Fixed bug where the aborted transfer flag was being ignored.
• Corrected a bug causing zero length binary values to be decoded as nil rather than a non-nil zero length slice.

v0.11.2

Clear connect timeout after connection established (#163)

v0.11.1: 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.

v0.11.0: 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.

v0.10.4

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