Smpplib

* Fix: split message detection 182 184 (fpalamour)

* New: allow customizing how error PDUs are handled (davidshepherd7)
* New: ignoring unknown optional parameters (davidshepherd7)
* New: add the option to create TLS/SSL sockets (davidshepherd7)
* Fix: the max check should include the NULL terminator (Pedrum Mohageri)
* Fix: not always setting the socket timeout (davidshepherd7)
* Fix: add mandatory parameters to GenericNack command (stefanruijsenaars)
* Fix: handle errors on PDU payload retrieval (stefanruijsenaars)

* New: add option to not use UDHI when splitting long SMS
* New: add `query_sm` & `query_sm_resp` support
* New: argument to make automatic `enquire_link` optional
* New: make logger specific to each `Client` instance by Lynesth
* Fix: incorrect `SMPP_UDHIEIE_PORT16` constant 81
* Fix: `enquire_link_resp` now echo original sequence
* Fix: wait for the full PDU before parsing 82
* Fix: add timeout to Client's properties 98 by Lynesth
* Fix: `DataSM` param naming error: `alert_on_message_delivery` 108 by nwnoga

* Fix: don't use `%` operator in logging

* Fix `TypeError` in `_generate_string_tlv` when encoding a value
* Support context manager interface, move `__del__` functionality to `__exit__`
* Change `callback_num` type to Octet String
* Add message state and network type constants
* Fix trailing NULL character in parsed octet strings
* Add optional fields for `deliver_sm` PDU (couldn't find them in specs but observed in real systems)
* Fix integers converted to strings
* Fix integer pack format for `size=4`, closes 51
* Fix typos in `SMPP_INT_NOTIFICATION_*` constants
* Raise an error if `message_payload` is used together with `short_message`

* Fix UCS-2 encoding: fixes 49 and 53