[bug#34523] Add tetrinet

[pkill9]

Tetrinet is a multiplayer tetris game. There are two versions: a command line 
implementation and a GTK implementation - this package is the command line 
implementation. http://tetrinet.or.cz/

The license is written in the README as

```
Distribution/license information
--------------------------------
This program is public domain, and may be modified and distributed without
limitation.
```

So I don't know what license to put it as, so I set it as 'expat'.

0001-gnu-Add-tetrinet.patch
Description: Text Data