Add integer formatting code for fixed-width signed arithmetic (2's complement)

GitHub fields:

assignee = 'https://github.com/lisroach'
closed_at = None
created_at = <Date 2017-06-05.04:03:26.700>
labels = ['interpreter-core', 'type-feature', '3.7']
title = "Add integer formatting code for fixed-width signed arithmetic (2's complement)"
updated_at = <Date 2017-06-13.03:25:21.157>
user = 'https://github.com/rhettinger'

bugs.python.org fields:

activity = <Date 2017-06-13.03:25:21.157>
actor = 'lisroach'
assignee = 'lisroach'
closed = False
closed_date = None
closer = None
components = ['Interpreter Core']
creation = <Date 2017-06-05.04:03:26.700>
creator = 'rhettinger'
dependencies = []
files = []
hgrepos = []
issue_num = 30571
keywords = []
message_count = 8.0
messages = ['295162', '295749', '295752', '295753', '295754', '295793', '295805', '295843']
nosy_count = 8.0
nosy_names = ['rhettinger', 'talin', 'pitrou', 'eric.smith', 'skrah', 'serhiy.storchaka', 'lisroach', 'cheryl.sabella']
pr_nums = []
priority = 'low'
resolution = None
stage = None
status = 'open'
superseder = None
type = 'enhancement'
url = 'https://bugs.python.org/issue30571'
versions = ['Python 3.7']