[Enhancement] Allow `Python: <class 'module'>` as argument to `pyimport`

With these methods:

```julia
pyimport((m, k)::Pair{Py}) = pyimport(string(m.__name__) => k)
pyimport((m, ks)::Pair{Py,<:Tuple}) = pyimport(string(m.__name__) => ks)
```
you can do something like
```julia
amodule = pyimport("amodule")
afunc = pyimport(amodule.submodule1.submodule2, "afunc")
```
You can use TAB completion at the REPL to get the submodules. This is more convenient than finding and typing the strings.

I don't know how robust `string(m.__name__)` is.