op, internal/ops: cleanups

Remove unnecessary fill when starting a recording in op.Record.
Have the exact number of possible stack kinds in ops.Ops.

Signed-off-by: Pierre Curto <pierre.curto@gmail.com>

op/op.go

@@ -153,8 +153,8 @@ func Record(o *Ops) MacroOp {
 		pc:  ops.PCFor(&o.Internal),
 	}
 	// Reserve room for a macro definition. Updated in Stop.
-	ops.Write(m.ops, ops.TypeMacroLen)
-	m.fill()
+	data := ops.Write(m.ops, ops.TypeMacroLen)
+	data[0] = byte(ops.TypeMacro)
 	return m
 }
 
@@ -162,17 +162,13 @@ func Record(o *Ops) MacroOp {
 // operation for replaying it.
 func (m MacroOp) Stop() CallOp {
 	ops.PopMacro(m.ops, m.id)
-	m.fill()
+	ops.FillMacro(m.ops, m.pc)
 	return CallOp{
 		ops: m.ops,
 		pc:  m.pc,
 	}
 }
 
-func (m MacroOp) fill() {
-	ops.FillMacro(m.ops, m.pc)
-}
-
 // Add the recorded list of operations. Add
 // panics if the Ops containing the recording
 // has been reset.