Accept dot-delimited schemaname.tablename 

Presently, blaze.SQL isn't accepting <schemaname>.<tablename> to identify tables outside the connecting user's own schema.  Parsing out a dot-delimited prefix and passing it to SQLAlchemy as "schema" fixes that.

I apologize for not including tests, but I haven't been able to get the tests to run.  Hopefully the small size of the pull request makes that OK.