Declare a class in a namespace using dot

**If you're reporting a bug, please include _input code_, _output documentation_,
a description of what you expected to happen, and what happened instead.**

* What version of documentation.js are you using?: 12.1.3
* How are you running documentation.js (on the CLI, Node.js API, Grunt, other?): no

I'm using the following JSDoc annotated JavaScript file:
**Input**
```js
/**
* @namespace
*/
const Extensions = {}

/**
* @class Extensions.Registry
*/
const Registry = Extensions.Registry = {}

/**
* @memberof Extensions.Registry
* @inner
* @function getGroups
*/
Registry.prototype.getGroups = () => {}
```

As you can see, I want to declare a namespace named `Extensions` and a class named `Registry` inside this namespace (using the dot notation).

Here's the result with `jsdoc`:

**Output** (using [jsdoc](https://www.npmjs.com/package/jsdoc))

As you can see the class `Registry` is in the namespace `Extensions` (as expected)

For reference, here's the result using `tsd-jsdoc`:

**TypeScript Definition** (using [tsd-jsdoc](https://www.npmjs.com/package/tsd-jsdoc))
```typescript
/**
* @namespace
*/
declare namespace Extensions {
/**
* @class Extensions.Registry
*/
class Registry {
/**
* @memberof Extensions.Registry
* @inner
* @function getGroups
*/
getGroups(): void;
}
}
```

And now, here's the result using `documentation`:

**Ouput** (using `documentation build file.js -f html`)

As you can see the class `Registry` is *not* in the namespace `Extensions` and the `getGroups` function is not attached to the `Registry` class.

**Ouput** (using `documentation lint file.js`)

```console
$ documentation lint file.js
/path/to/file.js
12:1 warning @memberof reference to Extensions.Registry not found

⚠ 1 warning
```

If I replace `Extensions.Registry` by `Extensions/Registry` then it's working in `documentation` but not `jsdoc`:

**Ouput** (using `documentation build file.js -f html` with `/` as a separator)

**Ouput** (using [jsdoc](https://www.npmjs.com/package/jsdoc) with `/` as a separator)

As you can see the class is named `Extensions/Registry` and is not part of the namespace `Extensions`.

I think we should use dot as a separator instead of slash to be consistent with JSDoc (or at least support both syntax).