Accelerate 'string'.format(value, ...) by using formatted string literals

GitHub fields:

assignee = 'https://github.com/serhiy-storchaka'
closed_at = None
created_at = <Date 2016-09-29.08:50:04.036>
labels = ['interpreter-core', '3.7', 'performance']
title = "Accelerate 'string'.format(value, ...) by using formatted string literals"
updated_at = <Date 2020-02-14.20:42:51.446>
user = 'https://github.com/serhiy-storchaka'

bugs.python.org fields:

activity = <Date 2020-02-14.20:42:51.446>
actor = 'BTaskaya'
assignee = 'serhiy.storchaka'
closed = False
closed_date = None
closer = None
components = ['Interpreter Core']
creation = <Date 2016-09-29.08:50:04.036>
creator = 'serhiy.storchaka'
dependencies = ['11549']
files = []
hgrepos = []
issue_num = 28308
keywords = []
message_count = 2.0
messages = ['277689', '277693']
nosy_count = 3.0
nosy_names = ['eric.smith', 'serhiy.storchaka', 'BTaskaya']
pr_nums = []
priority = 'low'
resolution = None
stage = None
status = 'open'
superseder = None
type = 'performance'
url = 'https://bugs.python.org/issue28308'
versions = ['Python 3.7']