The field list in docstrings may not always be contiguous

[naiquevin]

The current implementation assumes that all the field lists are added together but that may not always be the case. Sometimes the field lists could be interspersed by ReST directives such as .. versionchanged or .. versionadded as in these examples

• https://github.com/zzzeek/alembic/blob/master/alembic/operations.py#L725-L731
• https://github.com/zzzeek/alembic/blob/master/alembic/operations.py#L747-L757