Added clq_result::column_name() method

[dominicletz]

Hi there,

thanks for creating this great library. While using it I realized that I need access to the column names which where hidden in the meta data. I've added the column_name() method to expose them.

Thanks Dominic

[sandvige]

This code works well :)

[dominicletz]

As I'm still using this library I've found some critical bugs in it which surface under heavy load. I'm submitting them here