Rename ase_animation_direction_t enum values to match Aseprite's naming convention

[Pituivan]

I don't know if you will accept this since this would break API compatibility, but I wanted to at least fork this for my project because I find the direction enum constants too misleading, since there is one option missing and two of the existing ones have typos.

Basically this PR updates the enum to match the official options in Aseprite program.

• Renames ASE_ANIMATION_DIRECTION_FORWARDS to ASE_ANIMATION_DIRECTION_FORWARD.
• Renames ASE_ANIMATION_DIRECTION_BACKWORDS to ASE_ANIMATION_DIRECTION_REVERSE.
• Adds enum value ASE_ANIMATION_DIRECTION_PINGPONG_REVERSE.

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• Resolves [cute_aseprite] Typo in Tag Direction enum value name #442
• Resolves [cute_aseprite] Missing tag direction #443

[RobLoach]

I think this makes sense. You could likely go further and support backwards compatibility by adding a couple #defines too.

[Pituivan]

Good idea! I'm going to sleep but I'll do that tomorrow.

[RobLoach]

Should look something like this....

Suggested change

	struct ase_tag_t
	/* Backwards compatibility */
	#define ASE_ANIMATION_DIRECTION_FORWARDS ASE_ANIMATION_DIRECTION_FORWARD
	#define ASE_ANIMATION_DIRECTION_BACKWORDS ASE_ANIMATION_DIRECTION_REVERSE
	struct ase_tag_t

[Pituivan]

Sorry if I'm not implementing it right ahead! After a bad Arch update, my system decided to stop booting lol