Integer compression in 2.1

[westonpace]

Integer compression is very important. It's useful for integral types, decimal types, and temporal types. It can also benefit string / binary types as well as they store their offsets into integers. It can even benefit other encodings (such as structural encodings) that might need integer metadata arrays.

The state of the art appears to be a combination of bit packing, frame of reference, and delta encoding. We should implement these features in version 2.1 of Lance.