Make more use of convenience methods

FossilOrigin-Name: 89fbd7a1520ecb65809b4c1bd10006ce9bb3a662cb7e7804abaf85d1ee1da63a

src/Projectile.m

@@ -1,4 +1,8 @@
 #import "Projectile.h"
 
 @implementation Projectile
++ (instancetype)projectile
+{
+	return [[self alloc] init];
+}
 @end