Reduce Code Duplication

[ryanmrichard]

There's quite a bit of overlap in the two existing Allocator implementations. I'd like to try to reduce the copy/pasting as we'll likely be adding more Allocators down the line.

Original text:

Both non-direct and direct have to do the same wrapping around the input function, but this version handles the construction of the distarray properly for the direct case.

Originally posted by @jwaldrop107 in #102 (comment)