`JsonFileUpdater` class

[bleudev]

Add JsonFileUpdater class for simplifying worfking with json files.

file.json:

{
'hello': 'world'
}

f = JsonFileUpdater('file.json')
f['hello'] # 'world'
f['hi'] = 12

file.json after this code:

{
'hello': 'world',
'hi': 12
}

Also i suggest add support for with operator (json.loads -> change keys with [] operator -> json.dumps and write):

with f:
    f['hi'] = 12
    f['hello'] = 34.2

Also i suggest add support for custom loads() and dumps() functions and for indent (if custom loads() or dumps() are provided, they must support indent argument).

f = JsonFileUpdater('file.json', loads=ujson.loads, dumps=ujson.dumps)
f2 = JsonFileUpdater('file.json', indent=4)