Extend dict update to accept keyword args

[Quarz0]

Closes dict.update should return None, not self #18

dict.update() method should now accept keyword args just like dict(...)

Example of usage:

>> a = dict(a=1)
..
>> a.update(b=2)
..
None
>> a.update({'c': 3})
..
None
>> a
..
{"a": 1, "b": 2, "c": 3}

[laurentlb]

Thanks for the pull request!
Are there tests for this?

@brandjon, can you look at this PR? Both Chris and I are on leave this week.

[Quarz0]

I added some tests

[brandjon]

Roger, will review later today.

[laurentlb]

Looks good, thanks

If there's no more issue, I'm going to import this change.

[brandjon]

Approved, though I suggested one additional assertion for the unit test for Laurent to add as we're importing.

[laurentlb]

fyi, I added a few more tests here: 4d65f44