Implicit conversion of ints (and char const*) to handles?

Issue description

Is there a reason why handles are not implicitly constructible from ints (I may well have missed something obvious...)? e.g. something like

py::object func() {
    py::object tpl = py::make_tuple(1, 2);
    return tpl[1];
}

seems to have a clear meaning but fails to compile (error: invalid conversion from ‘int’ to ‘const char*’ (there are two overloads for operator[], one taking a handle and the other a const char*)).

If char const* was also implicitly convertible to handle then the second overload would not be necessary either.

For additional confusion, 0 is implicitly convertible to a handle (an invalid one: the null pointer).

Asked on gitter (a more specific version of this) but got no reply.

Reproducible example code

Include the above-mentioned code in python_example (replacing the add function there, and the m.def(... line).

Start with the python_example mentioned in the issue, replacing its add function and m.def(...) line with the reproducible code to confirm the compilation error. Then inspect the handle and operator[] overloads involved, and compare the current behavior with the requested implicit conversions; done means the intended behavior and its tests are established.