Pyvisa

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- add coverage
- add tox testing

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- Changed licence to MIT.
- Made determination of resource class even more careful.

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- Changed some __getattr__ to getattr in order to have working exceptions again
(e.g. timeouts) in vpp43
- Softened the test for "INSTR" even further. Introduced the "stb" property for
GPIB instruments.
- Changed "is not an INSTR" error to a warning.
- Added correct prefix for RPM in setup.cfg.

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- Mentioned possible AttributeError with viParseRsrcEx.
- Made secure against missing viParseRsrcEx.
- Removed superfluous calls to parse_resource_extended.
- setup.py Script can now handle installation with or without setuptools.
- setup.py: Switched to new distutils version.

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- New properties of SerialInstrument explained.
- Added many further properties to SerialInstrument.

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- Renamed timeout parameter in open() to open_timeout.
- Renamed Timeout parameter in open() to open_timeout.
- Added section about SerialInstrument.
- Added class SerialInstrument. Made termination characters even more robust.