Minor Description
When having a lot of columns grouped by name I've found that it would be very useful to be able to scan them using multiple prefixes, allowing to fetch specific groups in one scan, without fetching the entire row. This is impossible to achieve using a FilterList, so I've added such support to the existing ColmnPrefixFilter while keeping backward compatibility.
The attached patch is based on 0.90.4, I noticed that the 0.92 branch has a new method to support instantiating filters using Thrift. I'm not sure how the serialization works there so I didn't implement that, but the rest of my code should work in 0.92 as well.