README.md: avoid []byte -> string allocation/copy (coocood#98)

FreeCache invests a lot of effort to minimize GC overhead, yet the README example has a case where a (potentially very large) copy is made just as part of a `fmt.Println` call. With this change, it uses `fmt.Printf("%s\n", ...)`, which should be used in any case involving `Println` and a `[]byte` that's intended to be interpreted as string data.

Change-Id: I01e6067e3c2da12dfd75e391728265b749b848ca

README.md

@@ -44,7 +44,7 @@ got, err := cache.Get(key)
 if err != nil {
     fmt.Println(err)
 } else {
-    fmt.Println(string(got))
+    fmt.Printf("%s\n", got)
 }
 affected := cache.Del(key)
 fmt.Println("deleted key ", affected)

cache.go

@@ -78,9 +78,7 @@ func (cache *Cache) Touch(key []byte, expireSeconds int) (err error) {
 func (cache *Cache) Get(key []byte) (value []byte, err error) {
 	hashVal := hashFunc(key)
 	segID := hashVal & segmentAndOpVal
-	cache.locks[segID].Lock()
 	value, _, err = cache.segments[segID].get(key, nil, hashVal, false)
-	cache.locks[segID].Unlock()
 	return
 }
 
@@ -96,9 +94,7 @@ func (cache *Cache) Get(key []byte) (value []byte, err error) {
 func (cache *Cache) GetFn(key []byte, fn func([]byte) error) (err error) {
 	hashVal := hashFunc(key)
 	segID := hashVal & segmentAndOpVal
-	cache.locks[segID].Lock()
 	err = cache.segments[segID].view(key, fn, hashVal, false)
-	cache.locks[segID].Unlock()
 	return
 }