GitLab

Fix spelling

This commit also adds `doc()` to `object_api` as a shortcut for the
`attr("__doc__")` accessor.

The module macro changes from:
```c++
PYBIND11_PLUGIN(example) {
    pybind11::module m("example", "pybind11 example plugin");
    m.def("add", [](int a, int b) { return a + b; });
    return m.ptr();
}
```

to:

```c++
PYBIND11_MODULE(example, m) {
    m.doc() = "pybind11 example plugin";
    m.def("add", [](int a, int b) { return a + b; });
}
```

Using the old macro results in a deprecation warning. The warning
actually points to the `pybind11_init` function (since attributes
don't bind to macros), but the message should be quite clear:
"PYBIND11_PLUGIN is deprecated, use PYBIND11_MODULE".

This adds automatic casting when assigning to python types like dict,
list, and attributes.  Instead of:

    dict["key"] = py::cast(val);
    m.attr("foo") = py::cast(true);
    list.append(py::cast(42));

you can now simply write:

    dict["key"] = val;
    m.attr("foo") = true;
    list.append(42);

Casts needing extra parameters (e.g. for a non-default rvp) still
require the py::cast() call. set::add() is also supported.

All usage is channeled through a SFINAE implementation which either just returns or casts. 

Combined non-converting handle and autocasting template methods via a
helper method that either just returns (handle) or casts (C++ type).

Add unit tests and documentation for the chrono cast.

Test compilation instructions for Windows were changed to use the
`cmake --build` command line invocation which should be easier than
manually setting up using the CMake GUI and Visual Studio.

On my system (Mac OS with custom Python installation) I had to add the ldflags argument to python-config to get things working.