Working with comments; round-trip support

In order to work with comments, you must work with the raw model.

Each node in the model has two special attributes: .wsc_before and .wsc_after. These attributes are a list of any whitespace or comments that appear before or after the node.

from json5.loader import loads, ModelLoader
from json5.dumper import dumps, ModelDumper
from json5.model import BlockComment
json_string = """{"foo": "bar"}"""
model = loads(json_string, loader=ModelLoader())
print(model.value.key_value_pairs[0].value.wsc_before)  # [' ']
model.value.key_value_pairs[0].key.wsc_before.append(BlockComment("/* comment */"))
dumps(model, dumper=ModelDumper()) # '{/* comment */"foo": "bar"}'

This section will be expanded with time, the API for working with comments will likely change alot in future versions.