Main: Avoid repeating up key press

It's important to rotate only once per press.
Main: use 32-bit ints for time and score

These values can get very large.
cBlock: Adjust straight block to stay within bounds
Refactor the drawing of squares to screen

Instead of cSquare calling screen.DrawSquare(), the owner of each cSquare
calls screen.DrawSquare(), so cSquare itself is independent of Screen.

Fewer function params being passed around.
Erase blocks at old positions
Screen: Fix SDL-based square drawing

Location and size args got deleted, causing a build error.
Main: Do not generate null-type blocks