Support doctest_global_setup

[twmr]

The doctest plugin in sphinx support specifying a code block in conf.py that is called at setup time

doctest_global_setup = '''
try:
    import pandas as pd
except ImportError:
    pd = None
'''

Support for specifying this code block somewhere should be added.

It can't be added to pytest.ini, because AFAIK it (or ini files in general) doesn't have support for multiline values. So probably it needs to be set in conftest.py. If anyone know how this can be done - please comment.

[twmr]

This is already supported by pytest, see https://docs.pytest.org/en/latest/doctest.html#doctest-namespace-fixture

[twmr]

I created a ticket, where I asked about implementation details of this feature in pytest-dev/pytest#7140