updates to example data, DataGeometry persistence, tests, requirements + other improvements

[paxtonfitzpatrick]

• updates to example data
  • recreate example data objects work with sklearn>=0.24, upload to Drive to make available
  • replaced file IDs in hypertools.tools.load to reference new versions
• updates to data I/O
  • HypertoolsIOError class for data loading/saving-related errors
  • refactor hypertools.tools.load.load and hypertools.datageometry.DataGeomtry.save to use pickle instead of deepdish -- more efficient, and allows dependency on deepdish to be removed, which makes Hypertools compatible with Python 3.9
  • leave compression argument in hypertools.datageometry.DataGeomtry.save for now, but issue FutureWarning if passed
  • hypertools.tools.load updates:
    • add legacy argument to load function to enable loading .geo files from old format
    • add _load_legacy function for loading legacy-format data using deepdish
    • rewrite _load_example_data function to load data in new format
    • rewrite _download_example_data function to write stream to file more safely & automatically clean up in case of error/interruption during write
    • raise more explicit/clear exceptions on various failure conditions
• updates to tests
  • add tests for Python 3.9
  • switch from conda to mamba for faster environment setup
  • run pytest with more verbose output
  • don't add arm64 architecture tests for now -- test_format_data.test_force_align() fails seemingly due to bug with Ubuntu Xenial version used by Travis
• other updates
  • bump min sklearn version in requirements.txt to 0.24
  • remove __future__ and builtins imports from code (no longer needed for Python 2/3 compatibility)
  • remove dependencies on six & future (no longer needed for Python 2/3 compatibility)
  • fix use of is to compare literals
  • update readme.md to reflect new requirements
  • add syntax highlighting to fenced code blocks
  • update test_format_data.test_force_align to check output shape against new shape of example data
  • bump version to 0.8.0

[paxtonfitzpatrick]

CI tests are passing on the head of my fork https://github.com/paxtonfitzpatrick/hypertools/runs/5164529608