Adding Caching Adapter, allows caching of _Role and _User queries (fixes #168) (#1664)

* Adding Caching Adapter, allows caching of _Role and _User queries.

src/Adapters/Cache/CacheAdapter.js

@@ -0,0 +1,27 @@
+export class CacheAdapter {
+  /**
+   * Get a value in the cache
+   * @param key Cache key to get
+   * @return Promise that will eventually resolve to the value in the cache.
+   */
+  get(key) {}
+
+  /**
+   * Set a value in the cache
+   * @param key Cache key to set
+   * @param value Value to set the key
+   * @param ttl Optional TTL
+   */
+  put(key, value, ttl) {}
+
+  /**
+   * Remove a value from the cache.
+   * @param key Cache key to remove
+   */
+  del(key) {}
+
+  /**
+   * Empty a cache
+   */
+  clear() {}
+}