Add support modified_time, created_time, and accessed_time

### What is the problem / feature ?

The `InMemoryStorage` class did not implement `url`, `modified_time`, `accessed_time`, or `created_time`

### How did it get fixed / implemented ?

- Added the ability to specify a `base_url` during instantiation if you want support for urls.
- Added timestamps for `modified/accessed/created`.
- Tests to support these new features.

### How can someone test / see it ?

- Instantiate `InMemoryStorage` and check the timestamps on the in-memory-files

*Here is a cute animal picture for your troubles...*

![pumpkindog](https://cloud.githubusercontent.com/assets/824194/4759790/50f0604c-5aea-11e4-9fb2-c2b306287923.jpg)
Leftovers from debugging.  I'll update this first thing tomorrow.
On Oct 23, 2014 9:00 PM, "Nick Presta" <notifications@github.com> wrote:

> In tests.py:
>
> > @@ -82,5 +84,62 @@ def test_all(self):
> >          self.assertEqual(self.storage.exists('dir/subdir/file2'), False)
> >          self.assertEqual(self.storage.listdir('dir/subdir'), [[], []])
> >
> > +    @override_settings(MEDIA_URL=None)
> > +    def test_url(self):
> > +        # main storage not instantiated with a base url so should raise not
> > +        # implemented.
> > +        storage = InMemoryStorage()
> > +
> > +        with self.assertRaises(ValueError):
> > +            arst = storage.url('file0')
>
> I missed this the first time, but we don't need the result to be assigned
> since we don't use it.
>
> —
> Reply to this email directly or view it on GitHub
> <https://github.com/waveaccounting/dj-inmemorystorage/pull/4/files#r19321186>
> .
>