io: add type-specific read/write methods

This seriously improves the serialization/deserialization performance for
several reasons:
 * no time spent in `binary` reflection
 * no memory allocations being made on every read/write
 * uses fast ReadBytes everywhere it's appropriate

It also makes Fixed8 Serializable just for convenience.

pkg/util/fixed8.go

@@ -5,6 +5,8 @@ import (
 	"errors"
 	"strconv"
 	"strings"
+
+	"github.com/CityOfZion/neo-go/pkg/io"
 )
 
 const (
@@ -109,6 +111,16 @@ func (f Fixed8) MarshalJSON() ([]byte, error) {
 	return []byte(`"` + f.String() + `"`), nil
 }
 
+// DecodeBinary implements the io.Serializable interface.
+func (f *Fixed8) DecodeBinary(r *io.BinReader) {
+	*f = Fixed8(r.ReadU64LE())
+}
+
+// EncodeBinary implements the io.Serializable interface.
+func (f *Fixed8) EncodeBinary(w *io.BinWriter) {
+	w.WriteU64LE(uint64(*f))
+}
+
 // Satoshi defines the value of a 'Satoshi'.
 func Satoshi() Fixed8 {
 	return Fixed8(1)