Opencl interop

[sakchal]

This PR introduces a suite of functions for the OpenCL specific function seen in the documentation. These functions written are the wrapper functions for the original C functions, and will be helping implement the OpenCL specific functions in the higher level. Additionally, this PR features the first commit that sets up the OpenCL interface functions, but future commits will also help solve the OpenCL interoperability functionality present in much of the

Introduces several functions such as:

• get_context
• get_queue
• get_device_id
• set_device_id
• add_device_context
• delete_device_context
• get_device_type
• get_platform

[sakchal]

Along with the initial pull request, I added another file within the "interface functions" directory titled interop.py along with some brief tests for the functions.

Within the interop.py file, lie several functions to ensure the interoperability of arrayfire and other libraries (numpy and pyopencl as of now):

• numpy_to_af_array
• af_to_numpy_array
• pyopencl_to_af_array