Font improvements, faded lines, simplified menu+quitting

Font improvements, faded lines, simplified menu+quitting

In-game scores are now displayed using the fond code, the
"score.png" graphic and show_digit() function got removed.

Add dkc2 font, and improve font and graphics code (image
width, image height, sprite width, simplified char search.

New draw_line_faded() method that draws a line with faded
colors, fixed old draw_line() code and make draw_line() a
macro that calls draw_line_faded().

Add support for quitting tennix by closing the tennix window.

Elektrons beatified, added faded line drawing. Move around
items in the menu, remove sound + racket animation.

Fade to black the menu when quitting.

Clean-up stuff in tennix.h.