Exposing nested public symbols in Module

Let's say I am using embind to define some bindings, and I have two different classes by the same name which I would like to expose:
```
namespace some_namespace1 {
class Logger {
public:
void log() {}
};
}
namespace some_namespace2 {
class Logger {
public:
void log() {}
};
}

EMSCRIPTEN_BINDINGS(MyBindings) {
emscripten::class_<::some_namespace1::Logger>("Logger")
.function("log", ::some_namespace1::Logger::log)
;
emscripten::class_<::some_namespace2::Logger>("Logger")
.function("log", ::some_namespace2::Logger::log)
;
}
```

If we do this, we get a runtime error, `Cannot register public name 'Logger' twice`, from [here](https://github.com/emscripten-core/emscripten/blob/0c5046e64a80038bece746e3fde832d3ec1e9401/src/embind/embind.js#L1983), when registering the class, because the `.Logger` property is already defined on the Module, and it is not a function overload with a different number of arguments.

This is solvable by adding a prefix when binding each class, like `emscripten::class_<::some_namespace1::Logger>("some_namespace1_Logger")`.

But I wonder if we could instead support nesting exposed symbols into sub-objects at the Module level. So you could do something like:

```
emscripten::class_<::some_namespace1::Logger>("some_namespace1.Logger")
.function("log", ::some_namespace1::Logger::log)
;
emscripten::class_<::some_namespace2::Logger>("some_namespace2.Logger")
.function("log", ::some_namespace2::Logger::log)
;
```

We'd need to accept the dot character in the legal name check [here](https://github.com/emscripten-core/emscripten/blob/0c5046e64a80038bece746e3fde832d3ec1e9401/src/embind/embind.js#L2489).

We'd also need some logic [here](https://github.com/emscripten-core/emscripten/blob/0c5046e64a80038bece746e3fde832d3ec1e9401/src/embind/embind.js#L145-L148) to recursively apply this to the Module, by something like these [suggestions](https://stackoverflow.com/questions/20424226/easy-way-to-set-javascript-object-multilevel-property).

---

I wonder if this is something we'd want to support? Are there places where this feature would make things very difficult?