created from a str or Path obj

packages to preserve compatibility with python 2. But py2-compat is no longer
a goal, so we can now use native namespace packages.

"T1w.json" is a valid sidecar file

metadata file name, as files within a BIDS data set may be sym-linked from
another file/directory structure (e.g. datalad/git-annex)

fslpy for the most part, so are being moved to fsleyes-widgets

atexit (settings)

queued task raises an error.

Without this any FSL call under Windows opens potentially multiple
transient console windows which is distracting and slows down
performance