Pymodbustcp

- Add timeout parameter to ModbusClient constructor (thanks to bonaime).

- Fix rx_byte_count check in ModbusClient class.

- Catch excepts on socket send/recv.
- Sphinx documentation include a quickstart and examples.

- Add unit test (see test/).
- Add params host/port/unit_id/debug on ModbusClient constructor.
- Add utils module for modbus data mangling.

- Fix "socket error" message when call open() on dual stack IPv6/4 host.
- Check rx byte count field in functions 1 to 4.
- Fix max bit number problem in functions 1 and 2 (from 125 to 2000).
- Add debug message, if _send() call on close socket.
- Rename module name from const to constants.
- Update MANIFEST.in to remove docs and examples from sdist archive.
- Update README.rst sample code for Python3.

- Now deal with IPv6 host.
- Fix Python3 issue in _crc().
- Improve modbus RTU receive code.
- Secure frame size before struct.unpack invocation.