Allow doctest to select tests via -m/--match option

GitHub fields:

assignee = None
closed_at = None
created_at = <Date 2020-12-31.19:18:13.625>
labels = ['type-feature', 'tests', '3.10']
title = 'Allow doctest to select tests via -m/--match option'
updated_at = <Date 2021-01-01.09:40:34.483>
user = 'https://github.com/costas-basdekis'

bugs.python.org fields:

activity = <Date 2021-01-01.09:40:34.483>
actor = 'costas-basdekis'
assignee = 'none'
closed = False
closed_date = None
closer = None
components = ['Tests']
creation = <Date 2020-12-31.19:18:13.625>
creator = 'costas-basdekis'
dependencies = []
files = []
hgrepos = []
issue_num = 42797
keywords = ['patch']
message_count = 3.0
messages = ['384132', '384142', '384158']
nosy_count = 3.0
nosy_names = ['tim.peters', 'steven.daprano', 'costas-basdekis']
pr_nums = ['24028']
priority = 'normal'
resolution = None
stage = 'patch review'
status = 'open'
superseder = None
type = 'enhancement'
url = 'https://bugs.python.org/issue42797'
versions = ['Python 3.10']