refactoring: add type for needle id, offset

later the type size can possibly be adjusted

weed/storage/needle/needle_value.go

@@ -1,9 +1,8 @@
 package needle
 
 import (
-	"strconv"
-
 	"github.com/google/btree"
+	. "github.com/chrislusf/seaweedfs/weed/storage/types"
 )
 
 const (
@@ -11,8 +10,8 @@ const (
 )
 
 type NeedleValue struct {
-	Key    Key
-	Offset uint32 `comment:"Volume offset"` //since aligned to 8 bytes, range is 4G*8=32G
+	Key    NeedleId
+	Offset Offset `comment:"Volume offset"` //since aligned to 8 bytes, range is 4G*8=32G
 	Size   uint32 `comment:"Size of the data portion"`
 }
 
@@ -20,9 +19,3 @@ func (this NeedleValue) Less(than btree.Item) bool {
 	that := than.(NeedleValue)
 	return this.Key < that.Key
 }
-
-type Key uint64
-
-func (k Key) String() string {
-	return strconv.FormatUint(uint64(k), 10)
-}