[Golly-test] Golly turns 20

This year is Golly's 20th anniversary (0.1 was released in July 2005)
so I thought it might be fun to do a special 5.0 release some time in
the next few months.  I've already created a new app icon (with the
help of Claude):

https://trevorrow.com/golly/golly_icon.svg

Other changes I've done so far:

https://sourceforge.net/p/golly/code/ci/master/tree/Help/changes.html

Further changes I'm hoping to do (no promises!):

* Support RLE files with @RULE data included at the end (to agree
with LifeViewer).  I think this is a nicer option to replace some
of the zip files like calcyman-primer.zip.

* Native support for Margolus neighborhood rules (probably add it
to the LtL algo rather than create a new algo).

* Spruce up the interface with nicer, larger icons for the toolbar buttons.
Increasing the width of the various bars to 48px would allow us to
use 32x32px icons.

If anybody has suggestions for the 5.0 release then now is the time
to make them.  I'm giving myself until the end of August to work on
Golly (and some of that time will be taken up trying to sell my house!).

Cheers to all, and much thanks for your contributions over the
last two decades!

Andrew