Replaced copyright magic numbers in intro.c with constants

[pkmnsnfrn]

Description

Changed some magic numbers to constants for readability.

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pkmnsnfrn

[GriffinRichards]

This might be better served by comments at the start of each case block? I feel like by moving the numbers away it actually makes the flow a little harder to understand at a glance (i.e. before it's clearer that default is going to run until state == 140)

If you feel strongly about defining constants for this then they should probably be an enum to enforce the order:

enum {
    COPYRIGHT_INITIALIZE,
    COPYRIGHT_START_FADE = 140,
    COPYRIGHT_START_INTRO,
};

[pkmnsnfrn]

I figured constants would be good for users trying to add functionality to skip the copyright screen, to make it clear that they need to jump to a specific state.

I'll do the enum change if you agree that constants are acceptable, I think the enum change is a good idea.