Fit column headers to their content

This change will add some options to make the rendering of the column headers customizable and to make theire size expand to the size of its content if specified through the corresponding option. Please consider merging.

Even if we were not in agreement about this i just wanted to let you know that i found a working solution which does not touch any default behaviour or changes anything except the corresponding options are specified. So there is no impact to the API just some added options.