Added MSET command

MSET command added. Requires all keys to have the same JSON Path, which might fit most use cases, but is a limitation.  Optionally we could make the path an array as well to support all use cases.

packages/json/lib/commands/MSET.spec.ts

@@ -0,0 +1,19 @@
+import { strict as assert } from 'assert';
+import testUtils, { GLOBAL } from '../test-utils';
+import { transformArguments } from './MSET';
+
+describe('MSET', () => {
+    it('transformArguments', () => {
+        assert.deepEqual(
+            transformArguments(['1', '2'], '$', [{ a: 1 }, { b: 2 }]),
+            ['JSON.MSET', '1', '$', '{ "a":"1" } ', '2', '$', '{ "b":"2"} ']
+        );
+    });
+
+    testUtils.testWithClient('client.json.mGet', async client => {
+        assert.deepEqual(
+            await client.json.mGet(["1", "2"], "$", [{ a: 1 }, { b: 2 }]),
+          [null, null]
+        );
+    }, GLOBAL.SERVERS.OPEN);
+});