The time for retransmitting a message was set before transfer was done. This ment that if the transfer speed is slow or the message is big then it would be possible to trigger a retransmit too early.
Closes https://github.com/espressif/esp-mqtt/issues/131
- Some PUBLISHED events would not be posted due to outbox messages being deleted before receiving PUBCOMP.
- Current pending_message is no longer used to check for acknowledgements, as it doesn't work with multiple or out of order messages.
Closes https://github.com/espressif/esp-mqtt/issues/132
