The prefix "lib" should not be included, per the documentation.

This was not caught in local tests as the fallback was always used
locally.

Patch courtesy of Guanbin Xu <xugb@mail.ustc.edu.cn>.

Initially supports the GPU information functions via:
- pysmctrl.get_gpc_info(dev_id)
- pysmctrl.get_tpc_info(dev_id)
- pysmctrl.get_tpc_info_cuda(cuda_dev_id)
All functions are extensively documented. See pysmctrl/__init__.py
for details.

Device partitioning functions have yet to be mapped into Python, as
these will require more testing.

As part of this:
- libsmctrl_get_*_info() functions have been modified to consistently
  return positive error codes.
- libsmctrl_get_tpc_info() now uses nvdebug-style device numbering and
  uses libsmctrl_get_gpc_info() under the covers. This should be more
  reliable.
- libsmctrl_get_tpc_info_cuda() has been introduced as an improved
  version of the old libsmctrl_get_tpc_info() function. This continues
  to use CUDA-style device numbering, but is now resiliant to CUDA
  failures.
- Various minor style improvements in libsmctrl.c