* Remove all usage of python2_3.py
Technically these functions were exported at the top level of the library, this removes them without warning... If we want to we can bring them back for there, but I honestly don't think its needed, as we are py3 only now and have been for multiple releases.
This may introduce a number of 'useless cast' or similar but those were always happening anyway
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* Update varname in hdf example to avoid collision with builtin
* Clean up some leftover comments surrounding imports of compat code
* Unnecessary string casts
* Additional unnecessary casts
* syntax error fix
* more unnecessary casts
* Yet more unnecessary casts
* Loads only data that is currently visible
* Downsamples to avoid plotting too many samples
* Loads data in chunks to limit memory usage during downsampling