A few notes on porting Tcl/Tk 8.6 → 9

I have been porting a small GUI game ~1400LOC from Tcl/Tk 8.6 → 9.

**Changes for 8.6 → 9**

I used ~ for $HOME a few times in one function, so had to change that.

When drawing canvas polygons I found I was getting a 1 pixel black outline
that is _not_ present in the 8.6 version. So it appears that the default for
outline has changed. I easily fixed this by adding `-outline ""` but didn't
spot this in the Tk 9 release notes.

The biggest amount of work was with the namespace change. So I had to change
a lot of `board::...` to `::board::...` and similar. This was tedious but
not difficult.

**Changes since I was changing things**

I switched from sourcing Tcl files to using `.tm` modules; much nicer.

I switched from PNG images to SVG; again, much nicer.

**Scaling**

For scaling I use this line:

`if {[info exists env(TK_SCALING)]} {tk scaling $env(TK_SCALING)}`

and have an environment variable `TK_SCALING` which I set to different
values on my desktop and laptop.

However this doesn't work when I put a Tcl/Tk app in a taskbar launcher so
I'm going to add scaling as a config option too.

See Tcl/Tk 8.6: https://github.com/mark-summerfield/gravitate-tcl
and Tcl/Tk 9: https://github.com/mark-summerfield/gravitate-tcl9

PS My ISP has now stopped supporting newsgroup access.
And a few years ago Google stopped supporting them.
I really wish there was a general Tcl/Tk mailing list that could
be used.