Comment columns for slim decision and query tables

This enhancement has been discussed before on pivotal as id 3562479 and topic "ignored columns" 
It was rated as nice, but not necessary. Comment columns are marked by starting the header with #. This is in conformance to comments used within slim script tables.

Unfortunately, I was not aware of the comment cells mentioned there when I started to implement this feature. Nonetheless, comment columns are more useful than comment cells in my current use case, since I generate wiki pages from Excel sheets.

If there were not much more effort to implement the feature than to pull in the two commits here I would be happy to see this feature in fitness in the future.

Thanks
Markus

![commentcolumnquerytable](https://f.cloud.github.com/assets/174919/2085381/ee5ee714-8e43-11e3-93c3-2c0f1d4172b5.png)