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This is a major rewrite, but the API is backward compatible.
* Extended functionality to support more Modbus function codes.
* Option to close the serial port after each call (useful for Windows XP etc).
* Diagnostic string output available (for support).
* Debug mode available.
* Improved __repr__ for Instrument instances.
* Improved Python3 compatibility.
* Improved validity checking for function arguments.
* The error messages are made more informative.
* The new example driver omegacn7500 is included.
* Unit tests included in the distribution.
* A dummy serial port for unit testing is provided (including recorded communication data).
* Updated documentation.