Reset negated state after each assertion

[bdsoha]

Reset negated state after each assertion.

Assuming:

def test():
    data = ['hello']

    # Using the `assert` keyword
    assert isinstance(data, list)
    assert len(data) == 1
    assert 'hello' in data
    assert 'world' not in data

    # Using expectations
    expect(data) \
        .to.be_a_list() \
        .and_to.have_len(1) \
        .and_not.contain('world') \
        .and_to.contain('hello') \

This will currently fail due to the chained functionally of .and_not.contain('world') maintaining the negated stated.