[Pas2js] Small tetris demo added

[Michael Van Canneyt]

Hi,

Because we all want to have fun programming from time to time, 
I added a simple tetris game to the pas2js demos.

You can find it in svn under demos/tetris.

I put it also online (the advantage of web programming: live demos!)

https://www.freepascal.org/~michael/tetris/

It is a simple algorithm which seems to work ok, I only know of 1 glitch.

If someone wants to make a version that just uses html & css, no canvas,
this should be easily accomplished: patches welcome :)

Enjoy!

Michael.