Unexpected type casting in insert_dataframe

[FedericoCeratto]

Hello and thanks for developing the driver.

insert_dataframe(...) is attempting to cast a string column into int. The column is a String in the database.
The raised exception ValueError: invalid literal for int() with base 10: ... does not clarify where the column definition came from and how to solve the problem.
The library version is 0.2.0 and the database connection is configured to use Numpy.

Thanks!