devel release 20240321a

[Jeremy Faden CS]

I've made development release 20240321a, which I hope will become the
next production release.  This fixes a long-lived bug that wasn't
pointed out until this week, where the "nearest neighbor spectrograms"
option in the preferences did nothing.  This works again, along with a
bunch of other minor new bugs and features like:

* getDataSet and getDataSets is now a proper Jython function, with trim
which will clip the data to the trim timerange and sortTime which
ensures the data is time-ordered.
* fixLayout(verticalSpacing='1em',horizontalSpacing='1em') is a proper
Jython function.
* imageDataSource will use "richPng" metadata to assign default axis
labels for old pngs and pngs created by other software containing
richPng metadata.
* write the .vap.zip is done with an atomic move operation, so that a
corrupt version isn't accidentally used.

Let me know what you think.  Your feedback guides Autoplot's
development!  See http://autoplot.org/devel/ for this release.

Jeremy