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/InMemoryCacheAdapter.js

@@ -0,0 +1,36 @@
+import {InMemoryCache} from './InMemoryCache';
+
+export class InMemoryCacheAdapter {
+
+  constructor(ctx) {
+    this.cache = new InMemoryCache(ctx)
+  }
+
+  get(key) {
+    return new Promise((resolve, reject) => {
+      let record = this.cache.get(key);
+      if (record == null) {
+        return resolve(null);
+      }
+
+      return resolve(JSON.parse(record));
+    })
+  }
+
+  put(key, value, ttl) {
+    this.cache.put(key, JSON.stringify(value), ttl);
+    return Promise.resolve();
+  }
+
+  del(key) {
+    this.cache.del(key);
+    return Promise.resolve();
+  }
+
+  clear() {
+    this.cache.clear();
+    return Promise.resolve();
+  }
+}
+
+export default InMemoryCacheAdapter;