[Maxima] Maxima 5.21 release branch scheduled for April 1

[Robert Dodier]

Hello,

time for the customary 1-month warning.
I'm planning to make a release branch for Maxima 5.21
on April 1 or shortly thereafter, with a stable release to
follow within a few weeks.
If there is some stuff you develpers want to get into
the next release, now is the time to do it.

Thanks to everybody for their efforts.

best

Robert Dodier