clan::GameTime fault

[rombust]

There is an issue with clan::GameTime.
If you sum 30 seconds of samples from GameTime::get_time_elapsed_ms(), this does not equal GameTime::get_current_time_ms()

Demonstrated by:

    game_time.update();
    static int total = 0;
    total += game_time.get_time_elapsed_ms();
    printf("%d\n", (int) ( game_time.get_current_time_ms() - total));

There is a fault with the usage of time_elapsed_ms_microsecond_adjustment.

This can be trivially fixed by having a "updated_current_time_ms" variable and the elapsed time is the delta from before it was set.

Unfortunately I currently don't have time to fix it.

[rombust]

Fixed - "Fix accuracy of clan::GameTime get_time_elapsed_ms() by separating the mathematics between microseconds and milliseconds to avoid cumulative rounding errors"