Exception when trying to acces submodules of Main

I was trying to explore what Python functions are available as submodules of `Main`, especially the `PyCall` module, but apparently that isn't possible? Or is this a bug?

```
Python 3.8.5 (default, Jul 27 2020, 08:42:51)
[GCC 10.1.0] on linux
Type "help", "copyright", "credits" or "license" for more information.
>>> from julia.api import Julia
>>> j=Julia()
>>> from julia import Main
>>> dir(Main)
['Base', 'Core', 'PyCall', '__doc__', '__loader__', '__name__', '__package__', '__spec__', '_julia']
>>> dir(Main.Base)
Traceback (most recent call last):
File "", line 1, in
File "/home/melis/.local/lib/python3.8/site-packages/julia/core.py", line 176, in __getattr__
return self.__try_getattr(name)
File "/home/melis/.local/lib/python3.8/site-packages/julia/core.py", line 191, in __try_getattr
if self._julia.isdefined(realname):
File "/home/melis/.local/lib/python3.8/site-packages/julia/core.py", line 645, in isdefined
raise ValueError(
ValueError: `julia.isdefined(name)` requires at least one dot in `name`.
>>>

```