Improve parsing of names with nicknames

[vaneseltine]

By treating the nickname as a field separator, a first/middle or middle/last split could potentially be maintained. Currently the nickname is invisible to the subsequent processing.

[vaneseltine]

@pytest.mark.xfail(
    raises=AssertionError,
    reason="Probably not, but add a placeholder to keep names separated",
)
def issue_5_leave_non_comma_placeholder_from_nicknames():
    name = Name("angua van (barky) uberwald")
    assert name.last == "uberwald"

[vaneseltine]

Cf. #38

[vaneseltine]

Single-string output and idempotence removed as design goal.