Make inspect.signature able to parse format strings.

GitHub fields:

assignee = None
closed_at = None
created_at = <Date 2020-05-01.15:20:47.363>
labels = ['type-feature', 'library', '3.9']
title = 'Make inspect.signature able to parse format strings.'
updated_at = <Date 2020-05-03.01:23:54.236>
user = 'https://github.com/anntzer'

bugs.python.org fields:

activity = <Date 2020-05-03.01:23:54.236>
actor = 'FFY00'
assignee = 'none'
closed = False
closed_date = None
closer = None
components = ['Library (Lib)']
creation = <Date 2020-05-01.15:20:47.363>
creator = 'Antony.Lee'
dependencies = []
files = []
hgrepos = []
issue_num = 40470
keywords = []
message_count = 1.0
messages = ['367852']
nosy_count = 3.0
nosy_names = ['eric.smith', 'Antony.Lee', 'FFY00']
pr_nums = []
priority = 'normal'
resolution = None
stage = None
status = 'open'
superseder = None
type = 'enhancement'
url = 'https://bugs.python.org/issue40470'
versions = ['Python 3.9']