fix example program

[San7o]

The example program at the beginning of the RGFW.h header
does not compile and contains logic flaws. This pull request fixes
them.

Specifically, the original example uses the function
RGFW_window_window_isKeyPressed in line 92 which does not
exist. This could be fixed with RGFW_window_isKeyPressed(win, RGFW_escape).

However, when the escape key is pressed, the inner
while loop breaks but the outer loop continues since the exit key
was never set. For this reason, RGFW_window_setExitKey(win, RGFW_escape)
was added and RGFW_window_isKeyPressed has been removed.

The pixel format was updated from the old name RGFW_formatRGBA
to RGFW_formatRGBA8.

Lastly, mixed tabs and spaces have been replaced with only tabs to
be consistent with the rest of the example.

[ColleagueRiley]

Looks good. Thanks for the fixes.