Embind documentation for smart pointers is out of date.

[Grayson]

I have been recently attempting to support communication between the JS and C++ layer of code and was following through the embind documentation. I ran into a problem when implementing smart pointers (shared_ptr). The documentation is, if not incorrect, then so minimal as to be misleading. I was able to find a solution for using smart pointers from the test suite, but I think some attention to the documentation would help alleviate problems for future developers.

Ideally, I think the documentation for smart pointers should convey the following information:

• A corrected example that calls smart_ptr_constructor with the appropriate parameters. I found that I needed or provide a name parameter as the first argument in my use case. This was not indicated by the documentation.
• An example of creating a smart pointer in Javascript.
• An example of passing a smart pointer from Javascript to C++.

I think that correcting any errors and providing examples in these areas would greatly lower the barrier to making use of smart pointers.

For further consideration, I also think a discussion on the parameters taken in smart_ptr_constructor and for what they are used, an example with a class that takes parameters in its constructor, an example of a class with multiple constructors, and some more discussion on unique pointers and smart_ptr_traits would be appreciated and make this portion of the documentation feel more complete.

[kripken]

This repo is just for the site itself, the docs are in the main emscripten repo. Best to file this there, and add the label "embind".