Use coroutine object or coroutine function instead of coroutine

GitHub fields:

assignee = None
closed_at = None
created_at = <Date 2018-09-20.15:22:10.069>
labels = ['type-feature', '3.8', 'docs']
title = 'Use coroutine object or coroutine function instead of coroutine'
updated_at = <Date 2018-09-24.05:11:58.864>
user = 'https://github.com/Windsooon'

bugs.python.org fields:

activity = <Date 2018-09-24.05:11:58.864>
actor = 'Windson Yang'
assignee = 'docs@python'
closed = False
closed_date = None
closer = None
components = ['Documentation']
creation = <Date 2018-09-20.15:22:10.069>
creator = 'Windson Yang'
dependencies = []
files = []
hgrepos = []
issue_num = 34753
keywords = ['patch']
message_count = 3.0
messages = ['325886', '325908', '325947']
nosy_count = 3.0
nosy_names = ['docs@python', 'yselivanov', 'Windson Yang']
pr_nums = ['9523']
priority = 'normal'
resolution = None
stage = 'patch review'
status = 'open'
superseder = None
type = 'enhancement'
url = 'https://bugs.python.org/issue34753'
versions = ['Python 3.8']