Add 'array_hook' for json module

GitHub fields:

assignee = 'https://github.com/etrepum'
closed_at = None
created_at = <Date 2019-04-27.01:56:58.658>
labels = ['extension-modules', 'type-feature', 'library', '3.9']
title = "Add 'array_hook' for json module"
updated_at = <Date 2019-06-26.20:17:12.204>
user = 'https://github.com/matomatical'

bugs.python.org fields:

activity = <Date 2019-06-26.20:17:12.204>
actor = 'terry.reedy'
assignee = 'bob.ippolito'
closed = False
closed_date = None
closer = None
components = ['Extension Modules', 'Library (Lib)']
creation = <Date 2019-04-27.01:56:58.658>
creator = 'matomatical'
dependencies = []
files = []
hgrepos = []
issue_num = 36738
keywords = ['patch']
message_count = 1.0
messages = ['340957']
nosy_count = 2.0
nosy_names = ['bob.ippolito', 'matomatical']
pr_nums = ['12980']
priority = 'normal'
resolution = None
stage = 'patch review'
status = 'open'
superseder = None
type = 'enhancement'
url = 'https://bugs.python.org/issue36738'
versions = ['Python 3.9']