Remiplement Add to use reflection.

Now it matters whether `FieldLabel`s are spelled correctly, but in return, we don't have to write and maintain that obnoxious `switch` statement.

koboldsim/cardtypes.go

@@ -9,7 +9,6 @@ import (
 var (
 	ErrOptionNotEnabled = errors.New("option not enabled")
 	ErrPolicyNotEnacted = errors.New("cannot unenact policy that is not enacted")
-	ErrNoFieldLabel     = errors.New("field does not exist")
 
 	// ErrUnimplemented and ErrKeepMessaage are "non-errors". They are used
 	// as special signals that the result needs to be handled in a special way;