Improve memoization section

resources.md

@@ -7,7 +7,7 @@
 
 #### Cache
 
-* [lru-cache](https://github.com/isaacs/node-lru-cache) – A `Map` cache that deletes the least-recently-used items.
+* [lru](https://github.com/chriso/lru) – A simple LRU cache supporting O(1) set, get and eviction of old keys.
 * [async-cache](https://github.com/isaacs/async-cache) – Cache your async lookups and don't fetch the same thing more than necessary.
 * [mem](https://github.com/sindresorhus/mem) - An optimization used to speed up consecutive function calls.
 

workflow/memoization.md

@@ -1,17 +1,17 @@
-# Memoization: Cache successive calls.
+# Memoization: Cache successive calls
 
 Just calculate the value of something once and reuse the value. This avoids the cost of recalculating the same value.
 
-If you need to control a set of small values, you can use a `Map`:
-
 ```js
-var cache = new Map()
-
+var cache = Object.create(null)
 var cityOne = 'Murcia'
 var cityTwo = 'Madrid'
 var routeName = `${cityOne}${cityTwo}`
-
 if (!cache.has(routeName)) cache.set(routeName, getDistance(cityOne, cityTwo))
 ```
 
-A more complex, but better solution, would be to control the size of the `Map`. One example would be to use an LRU cache.
+Notes that first line is `Object.create(null)`. This create a `Object` without `prototype`. because we want a pure object for be used as a Hash Table (with all the [prototypical method](https://developer.mozilla.org/es/docs/Web/JavaScript/Referencia/Objetos_globales/Object/prototype) missing).
+
+If you need more control about your cache, you can create it using Map or WeakMap structures. Specially use it when you want to remove items from the cache.
+
+[LRU](https://www.npmjs.com/package/lru) or [mem](https://www.npmjs.com/package/mem) are good high level libraries that implement this technique.