Multivalue Field can't remove values #22

Starting at line: https://github.com/versionone/VersionOne.SDK.Python/blob/master/v1pysdk/v1meta.py#L110

There is no code path that allows you to remove values from a multi value field.

As an API user
I want to set multi-value fields to exact values
So that assignment works as expected.

Given a Workitem with Owners = [user1, user2]
When I assign [user2, user3] to Owners
And commit
Then Owners should be [user2, user3]