Add Numpy, PIL, Scikit-Image support

[myselfhimself]

Matrix layout and (de)interleaving presets:
- [x] add presets to G'MIC module and add validator GmicImage class method

• set up Jupyter Lab document for simpler testing than Pytest and RFC-ing of presets to the numpy, PIL and and scikitimage communities
  - [x] parameters mutual-exclusion: prevent from/to_numpy_array parameters tuning (except for as_type) if a preset is used, raise GmicException in such cases

Numpy I/O support

- [x] add 'a': a third letter for the 'i'/'d' (de)interleaving option to have no effect on channels pixel format. 'a' for agnostic

• from_numpy() - deinterleaving input

  • code
  • docstring
  • pytest

• to_numpy() - interleaving output

  • code
  • docstring
  • pytest

• solidify GmicImage.to_numpy_helper()

  • remove preset= parameter
  • up-to-date C docstring
  • permute='xyzc' parameter
    • cpython code
    • pytest
  • interleave=False:bool parameter
    • cpython code
    • pytest
  • squeeze_shape=False:bool parameter
    • cpython code
    • pytest
  • astype=None:numpy.dtype parameter
    • cpython code
    • pytest

• solidify GmicImage.from_numpy_helper()

  • up-to-date C docstring
  • deinterleave=False:bool parameter
    • cpython code
    • pytest
  • permute='xyzc':bool parameter
    • cpython code
    • pytest

Scikit-image I/O support

• Scikit-image support documentation section
• from_scikit()
  • pure-python code
  • well-documented C string
  • cpython code
  • pytest
  • advanced pytest with skimage module
• to_scikit()
  • pure-python code
  • well-documented C string
  • cpython code
  • pytest
  • advanced pytest with skimage module

PIL I/O support

• PIL support documentation section
• from_PIL()
  • pure-python code
  • well-documented C string
  • cpython code
  • pytest (PIL output to image+G'MIC output to image + pixel-to-pixel comparisons)
• to_PIL()
  • pure-python code
  • well-documented C string
  • cpython code
  • pytest (PIL output to image+G'MIC output to image + pixel-to-pixel comparisons)

[myselfhimself]

Let me try to write the pytest cases for input-output conversion in pure Python / Numpy to the various toolkits and code the conversion operations in C/Python when they work... (scaffolding in the biological cellular sense)..

[myselfhimself]

An early presets design specification (premute, interleave) config tuples has been submitted for RFC in our lab:
https://colab.research.google.com/drive/1bZzJDqdEvtoIgGrx3GchPwu95SgFM8D7?usp=sharing (public Google Colab sheet)

I might push this sheet on Twitter and Pixls.us for more RFC, when there are working examples for each preset (eg. pure Python transposes from vanilla from_/to_numpy_array() calls in order to reach a display in PIL/ScikitImage/Numpy-Matplot).

[myselfhimself]

In gmic-2.9.1-alpha1, presets and options are mixing up their effects. Will be fixed (checkbox added in the TODO above)

[myselfhimself]

Created an editable RFC of conversion presets on Google Colab, also backed up here on Github. It both gives preset specifications and code blocks exemplify and testing them.
Uploading fresher and fresher wheels to pypi.org will allow to write those tests within the notebook.

[myselfhimself]

gmic-py 2.9.1 alpha 2 with PIL I/O and solidified numpy I/O is released at: https://pypi.org/project/gmic/2.9.1a2/

• will update the docs (Numpy support page) and add a new PIL support page as well on the https://gmic-py.readthedocs.io/ website
• tutorials and examples are slated for November-December 2020 instead

[myselfhimself]

Rearranged TODO list into 3 distinct numpy, PIL, scikit sections at the top of this issue

[myselfhimself]

• discarded to_numpy_gmic and from_numpy_gmic converters (ie. for non (de)-interleaved non-permuted numpy<->g'mic array conversion), in favour of just to_/from_numpy_helper's default parameters as they are now (and locked in their behaviour by current unit tests..)
• discarding the idea of module-level per-toolkit preset constants.. those string constants in a home-made format could have been replaced by dictionaries for calling to_/from_numpy_helper (ie. function kwargs).. but I am chosing to keep things even simpler for now, especially I do not want to force numpy import at module-instantiation time, and the PIL preset would require this (ie. casting to uint8 using numpy.uint8)

[myselfhimself]

Come on come on!!! A few TODO checkboxes remaining and we are close to the goal!!!