Implement crouching (#62)

Reviewed-on: #62
Co-authored-by: Álex Román Núñez <eirexe@eirteam.moe>

src/fighter/animation.rs

@@ -84,6 +84,9 @@ pub enum AnimKind {
     AirDodge,
     Fall,
     Turn,
+    CrouchEnter,
+    CrouchIdle,
+    CrouchExit,
 
     FlinchGround,
     FlinchAir,