fix(ejson): support array for replacer parameter in EJSON.stringify

* Fix EJSON.stringify if replacer is array (not function)

Currently, passing an array form of the `replacer` parameter of EJSON.stringify will not work, despite the documentation saying that it should work.  The cause is that the current implementation checks whether `replacer` is of type `object`, and if it is then it assumes that the `replacer` parameter is really the `options` parameter (meaning that `replacer` and `space` have been omitted by the user).  This logic breaks when `replacer` is an array (which is an `object` too). 

To fix this problem I added a check using `Array.isArray` so the replacement above will only happen if `replacer` is an object that's not an array. 

While I was at it, I also changed the weird (and eslint-defying) use of assignment expressions ( `if (...) (options = space), (space = 0);` format to a more conventional statement form of assignment.

* Added test for array-valued replacers

Made sure that array-valued replacers work correctly. Also making sure that function-valued replacers work too.

* Fixed bugs in test cases

* removed unnecessary async function to fix Node 6

* EJSON serializing of ObjectID (capital D) + perf fix

While I was testing my other fix, I found and fixed two other problems with EJSON serialization:
* Fixes #303 - ObjectID (capital "D") instances can't be serialized to Extended JSON
* Fixes #302 - Extended JSON serializer runs twice for every nested document 

I also noticed two other potential problems that I didn't know how to fix, so I added TODO comments in this commit for tracking later.

If you want me to split these changes up into separate PRs from my original commits, I'm happy to do so-- just let me know.

* Update EJSON tests for ObjectId and ObjectID

Added tests to ensure that EJSON support for ObjectId works for three variations: 
* import ObjectId from 'bson';
* import ObjectID from 'bson'; 
* `import ObjectID from 'mongodb';  // verifies the fix for #303`

* fixed browser test

Ignoring the require('mongodb').ObjectID tests on the browser tests where that package is not available.

* another fix for browser tests

* another try to avoid browser test import error

* reverted changes moved to other PRs

lib/extended_json.js

@@ -169,9 +169,15 @@ const BSON_INT32_MAX = 0x7fffffff,
  * console.log(EJSON.stringify(doc));
  */
 function stringify(value, replacer, space, options) {
-  if (space != null && typeof space === 'object') (options = space), (space = 0);
-  if (replacer != null && typeof replacer === 'object')
-    (options = replacer), (replacer = null), (space = 0);
+  if (space != null && typeof space === 'object') {
+    options = space;
+    space = 0;
+  }
+  if (replacer != null && typeof replacer === 'object' && !Array.isArray(replacer)) {
+    options = replacer;
+    replacer = null;
+    space = 0;
+  }
   options = Object.assign({}, { relaxed: true }, options);
 
   const doc = Array.isArray(value)

test/node/extended_json_tests.js

@@ -253,4 +253,22 @@ describe('Extended JSON', function() {
     expect(result.test).to.equal(34.12);
     expect(result.test).to.be.a('number');
   });
+
+  it('should work for function-valued and array-valued replacer parameters', function() {
+    const doc = { a: new Int32(10), b: new Int32(10) };
+
+    var replacerArray = ['a', '$numberInt'];
+    var serialized = EJSON.stringify(doc, replacerArray, 0, { relaxed: false });
+    expect(serialized).to.equal('{"a":{"$numberInt":"10"}}');
+
+    serialized = EJSON.stringify(doc, replacerArray);
+    expect(serialized).to.equal('{"a":10}');
+
+    var replacerFunc = function (key, value) { return key === 'b' ? undefined : value; }
+    serialized = EJSON.stringify(doc, replacerFunc, 0, { relaxed: false });
+    expect(serialized).to.equal('{"a":{"$numberInt":"10"}}');
+
+    serialized = EJSON.stringify(doc, replacerFunc);
+    expect(serialized).to.equal('{"a":10}');
+  });
 });