absolute_path UX, improve test coverage

absolute_path: return UNC paths unmodified, print invalid path if canonicalize fails

add subprocess_run test of env=

test fileio.which: accommodate Matlab on MacOS

use CMake to extract zstd

Most of our users will have CMake already, at least as likely as having zstd without having to use an intermediate temporary file. So it's faster and robust.

improve test coverage, cleanup lint

Improve auto-linter, resolve minor issues thereby discovered

which: streamline logic

allow fpath to be a scalar or array

[h5,nc]save: allow bare filename

[h5,nc]save: allow plain filename without folder

ci: update actions

HDF5 scalar write, Matlab >= R2020b

Matlab doesn't have a high-level function to write scalar HDF5 dataset, so we added it to our h5save.

To avoid excess code, we put enhanced argument checks in stdlib.hdf5nc functions that require Matlab >= R2020b.

add fileio.sha256sum

v4.0.1

add fileio.sha256sum

reorganized as stdlib

combined a few complimentary libraries into this stdlib.

import hdf5nc.* => import stdlib.hdf5nc.*

bugfix: h5write size type

Some functions may pass a non-double size to h5write, which matlab needs, despite the data inherently being integer.
This casts size to double.

emptyness passthrough

the non-writing functions now return empty-like values when empty filename or other parameters are passed in. This seems to be a better match to expected behavior of other Matlab functions: empty in, empty out.

• {h5,nc}exist
• {h5,nc}size
• {h5,nc}variables

Separately, we moved CI to Azure since Travis-CI now has quotas, even for open-source projects.