BUG: specifying multiple columns as primary keys broken in io.sql.get_schema

[jorisvandenbossche]

See http://stackoverflow.com/questions/30911299/get-schema-multiple-primary-keys

I think this still works for the fallback sqlite version, but not for the new sqlalchemy implementation. in PrimaryKeyConstraint, the columns should be feeded as separate positional arguments instead of a list (https://github.com/pydata/pandas/blob/master/pandas/io/sql.py#L837). So just needs an unacking *.