drop #each API

When `#get` or `#set` are called during iteration, it possibly ends up with an
invalid state. And it's hard to support stable `#each` with current
implementation.

index.js

@@ -205,33 +205,21 @@
     },
 
     /**
-     * return array of keys
+     * return array of keys in least recently used order
      * @return {Array}
      */
     keys: function () {
-      var i = 0
+      var count = 0
+        , tail = this._tail
+        , head = this._head
         , keys = new Array(this._len);
 
-      this.each(function (val, key) {
-        keys[i++] = key;
-      });
-
-      return keys;
-    },
-
-    /**
-     * call function in least recently used order
-     * the most recently used cache will be executed last
-     * @param {Function}
-     * @param {Object}
-     */
-    each: function (fn, context) {
-      var tail = this._tail
-        , head = this._head;
       for (var i = tail; i < head; i++) {
         var entry = this._byOrder[i];
-        if (entry) fn.call(context, entry.val, entry.key);
+        if (entry) keys[count++] = entry.key;
       }
+
+      return keys;
     },
 
     /**

test/simple-lru.js

@@ -127,24 +127,6 @@ describe('SimpleLRU', function () {
     })
   })
 
-  describe('#each', function () {
-    it('should loop through in least recently used order', function () {
-      var cache = new SimpleLRU(3)
-      cache.set('b', 'B')
-      cache.set('a', 'A')
-      cache.get('b')
-      cache.set('c', 'C')
-      var keys = ['a', 'b', 'c']
-      var values = ['A', 'B', 'C']
-      var i = 0
-      cache.each(function (val, key) {
-        expect(val).to.be(values[i])
-        expect(key).to.be(keys[i])
-        i++
-      })
-    })
-  })
-
   describe('#length', function () {
     it('should return total number of cache', function () {
       var cache = new SimpleLRU(3)