printer: use tabwriter to align instructions (#8)

internal/prnt/printer.go

@@ -4,6 +4,7 @@ package prnt
 import (
 	"bytes"
 	"fmt"
+	"io"
 )
 
 // Generator provides convenience methods for code generators. In particular it
@@ -15,6 +16,11 @@ type Generator struct {
 	err error
 }
 
+// Raw provides direct access to the underlying output stream.
+func (g *Generator) Raw() io.Writer {
+	return &g.buf
+}
+
 // Printf prints to the internal buffer.
 func (g *Generator) Printf(format string, args ...interface{}) {
 	if g.err != nil {