Correct handling of IN operator argument

Filter with IN operator was not working, due to i,j,k being treated as a
single string. Added casting to address this, and extended a test to
check it.
Auth - parameter to override db table name
Merge pull request #116 from gobelinus/master

Auth - parameter to override db table name
Adding test for user db table.
Removed cast to int from IN list

Forgot that IN can also be used with lists of non-integer values. Thanks
to reminder by coleifer, removed cast, added test for non-integer lists.
Merge pull request #115 from cpbotha/in_operator_fix

Correct handling of IN operator argument
Merge branch 'master' of https://github.com/coleifer/flask-peewee
Merge branch 'master' into hans