Awkward Array GPU Kernels

The goal of this project is to add a GPU backend to Awkward Array 1.x. With such a backend, the library would have a unique capability of processing complex, JSON-like data that is wholly resident on GPUs, in an efficient way, without specialized compilation or even leaving the Python prompt. Deployment is a major part of this project and the aim is to have a seamless transition from the CPU backend to the GPU backend, with the dependent projects having to make minimal changes to accomodate for the new backend.