## Describe the changes
This PR adds the capability to pin host memory in golang bindings
allowing data transfers to be quicker. Memory can be pinned once for
multiple devices by passing the flag
`cuda_runtime.CudaHostRegisterPortable` or
`cuda_runtime.CudaHostAllocPortable` depending on how pinned memory is
called
## Describe the changes
This PR adds multi gpu support in the golang bindings.
Tha main changes are to DeviceSlice which now includes a `deviceId`
attribute specifying which device the underlying data resides on and
checks for correct deviceId and current device when using DeviceSlices
in any operation.
In Go, most concurrency can be done via Goroutines (described as
lightweight threads - in reality, more of a threadpool manager),
however, there is no guarantee that a goroutine stays on a specific host
thread. Therefore, a function `RunOnDevice` was added to the
cuda_runtime package which locks a goroutine into a specific host
thread, sets a current GPU device, runs a provided function, and unlocks
the goroutine from the host thread after the provided function finishes.
While the goroutine is locked to the hsot thread, the Go runtime will
not assign other goroutines to that host thread
