Sensirion-shdlc-driver

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- Move parts of ``ShdlcDevice`` into new base class ``ShdlcDeviceBase``

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- Make signature and version offset configurable for ``ShdlcFirmwareImage``

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- Add property ``is_open`` to ``ShdlcPort``, ``ShdlcSerialPort`` and
``ShdlcTcpPort``
- Improve/extend documentation

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- Add ``ShdlcTcpPort`` class to communicate with SHDLC devices through TCP/IP
- Add property ``start_received`` to ``ShdlcSerialMisoFrameBuilder``
- Add methods ``open()`` and ``close()`` to the ``ShdlcPort`` interface
- Add parameter ``do_open`` to constructor of ``ShdlcSerialPort`` to allow
creating ``ShdlcSerialPort`` instances without opening the port yet
- Add property ``additional_response_time`` to ``ShdlcSerialPort``
- Improve timeout calculation of ``ShdlcSerialPort`` to fix possible response
timeout errors
- Make ``FirmwareUpdate`` failing early if the bitrate cannot be changed

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- Add optional dependency ``intelhex`` for performing firmware updates
- Add bootloader commands: ``ShdlcCmdBootloaderBase``,
``ShdlcCmdEnterBootloader``, ``ShdlcCmdFirmwareUpdateStart``,
``ShdlcCmdFirmwareUpdateData``, ``ShdlcCmdFirmwareUpdateStop``
- Add exceptions for the firmware updater:
``ShdlcFirmwareImageSignatureError``,
``ShdlcFirmwareImageIncompatibilityError``
- Add classes to perform firmware updates over SHDLC: ``ShdlcFirmwareImage``,
``ShdlcFirmwareUpdate``
- Add property ``lock`` to the ``ShdlcPort`` interface to allow locking the
port from outside the class

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- Initial release