Add support to json.load to read from a string or Path object containing the path to a json file. Many libraries (like Numpy) support this behavior.

This expands the API where json.load now only accepts open file objects to support str and pathlike objects. This was discussed in https://mail.python.org/pipermail/python-ideas/2017-March/045303.html where there were alternatives proposed as below : 

with path.open() as f: obj = json.load(f)

some_path.write_text(json.dumps(obj), encoding='utf8')
json.loads(some_path.read_text(encoding='utf8'))

Also supporting str and pathlib passes responsibility to json.load to open them and also close them properly? I think this needs a python-ideas discussion if the proposal has something to add other than the previous thread where many alternatives were mentioned for terse code.

I close this because PR is closed already, and same idea
was discussed on -ideas ML.