Minor bugfixes, as well as a few small feature additions:
- add a ``read_csv()`` function to ``abutils.core.sequence``
- refactor the ``abutils.core.pair.Pair`` object:
- new ``heavies`` and ``lights`` properties
- ``vrc01_like`` is a standalone function in ``abutils.core.pair`` rather than a method of ``Pair``
- ``vrc01_like()`` now has an additional argument: ``loose``. If ``True``, a ``Pair`` will be considered VRC01-like if any of the chains in ``heavies`` or ``lights`` meet the VRC01-like criteria. If ``False``, the primary ``heavy`` and ``light`` chains must meet the criteria.