Implement inspect request

Pressing Shift+Tab brings up the inspector window in the notebook, which shows documentation of the function where the cursor is at. Input code must be parsed to correctly identify the symbol that documentation should be displayed for.

Example:

Placing the cursor in getprofile shows its documentation (correctly ignores previous lines):

Placing the cursor after getrecursionlimit’s opening bracket, it shows documentation of getrecusrionlimit(correctly ignores getprofile symbol):

This is the input that xeus receives:

code: a=5
b=10
sys.getprofile(sys.getrecursionlimit()
cursor_pos: 24
detail_level: 0```

[dgobbi]

Regarding stubs for VTK, once the docstrings are fixed, someone could write a Python utility script to introspect the wrappers and generate the stubs. I’m not keen on having the stubs be part of the VTK distribution (the wrappers are already too heavy), but having a script that generates the stubs on demand seems like a good solution.

[dgobbi]

PEP484 is useless in terms of describing the implementation (since it only talks about syntax). But after looking at Python’s funcobject.c the implementation seems pretty straightforward. It should be possible to add an __annotations__ dict to PyVTKMethodDescriptor.cxx alongside the existing __doc__ attribute.