Add get/set_global_value/array methods
Add get/set_global_value/array methods

- These provide convenient ways to set and get global variables
  without needing to use the CUDA Driver API.
  They also check that the type size matches, making them safer.
- Also adds a size parameter to get_global_ptr to allow retrieving
  the size of a global variable.

NVIDIA/jitify,NVIDIA/jitify