[Tux4kids-tuxtype-dev] Tux Math now GPLv3 or later

[David Bruce]

Hi everyone,

I have finished cleaning up all the copyright and license notices in
Tux Math, and the code is now uniformly licensed as "GPL3 or later".
In case anyone wants to use previous versions of our code in a GPL2
project, there is a notice under doc/ stating where to get
tuxmath-1.8.0.

Tux Typing and T4K_Common will be reviewed and tidied up in due course.

Best,

David