* Create Attocube directory in instrument_drivers
* Create empty __init__.py
* Create Attocube_ANC300.py module file
* Add initial code to Attocube_ANC300.py

Add basic examples notebook for Attocube ANC300 driver. To be expanded.

Remove line logging to error when the error check field from an instrument answer is 'ERROR'.
Unnecessary since we raise an Exception anyways.
These Exceptions can now be dealt with in a try .. except block without polluting the error log (e.g. in ANC300.__init__()).

Remove loop getting all parameters from instrument and submodules.
Use update=True in print_readable_snapshot instead.

Attempt to fix error 'Unexpected indentation' from sphinx in Travis build.
Wrap long docstring lines with single tab.

Integrate microsoft#859 changes to ask_raw in VisaInstrument in overriden ask_raw function.
Should fix Codacity 'String statement has no effect'warning.

Errors when getting frequency parameter with some ANC300 units.
The response to such queries ends with 'H\r\nOK' or 'Hz\r\nOK'.
Fixed by allowing unit keyword parameter of ans_parser to accept lists.
Refactor ans_parser accordingly.
Change definition of frequency parameter to call ans_parser with keyword
unit=['Hz','H'].