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

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

spec/InMemoryCacheAdapter.spec.js

@@ -0,0 +1,59 @@
+var InMemoryCacheAdapter = require('../src/Adapters/Cache/InMemoryCacheAdapter').default;
+
+describe('InMemoryCacheAdapter', function() {
+  var KEY = 'hello';
+  var VALUE = 'world';
+
+  function wait(sleep) {
+    return new Promise(function(resolve, reject) {
+      setTimeout(resolve, sleep);
+    })
+  }
+
+  it('should expose promisifyed methods', (done) => {
+    var cache = new InMemoryCacheAdapter({
+      ttl: NaN
+    });
+
+    var noop = () => {};
+
+    // Verify all methods return promises.
+    Promise.all([
+      cache.put(KEY, VALUE),
+      cache.del(KEY),
+      cache.get(KEY),
+      cache.clear()
+    ]).then(() => {
+      done();
+    });
+  });
+
+  it('should get/set/clear', (done) => {
+    var cache = new InMemoryCacheAdapter({
+      ttl: NaN
+    });
+
+    cache.put(KEY, VALUE)
+      .then(() => cache.get(KEY))
+      .then((value) => expect(value).toEqual(VALUE))
+      .then(() => cache.clear())
+      .then(() => cache.get(KEY))
+      .then((value) => expect(value).toEqual(null))
+      .then(done);
+  });
+
+  it('should expire after ttl', (done) => {
+    var cache = new InMemoryCacheAdapter({
+      ttl: 10
+    });
+
+    cache.put(KEY, VALUE)
+      .then(() => cache.get(KEY))
+      .then((value) => expect(value).toEqual(VALUE))
+      .then(wait.bind(null, 50))
+      .then(() => cache.get(KEY))
+      .then((value) => expect(value).toEqual(null))
+      .then(done);
+  })
+
+});