Updating math_ptx submodule

- Fixes problem with erf
Adding abs support for complex numbers
Merge pull request #226 from pavanky/cplx

Abs support for complex numbers
Compilation fix for cpu complex.hpp
2d convolve performance improvements

changed the shared memory loading access pattern in 2d convolve
kernel for cuda and opencl backends
Merge pull request #227 from 9prady9/conv2d_perf_fixes

2d convolve performance improvements
Added pinned memory functionality

* Moved alloc and pinned out of array class. Now use af::alloc or af::pinned.
* Fixed warning in cuda JIT for printf
Fixed potential memory leaks. Each array allocated with new [n] must be deallocated using delete [].
Merge pull request #229 from shehzan10/devel

Added pinned memory creation
Updating CONTRIBUTING.md
Added warning messages for when submodules are not cloned
Fix signed to unsigned comparision warning.
Merge pull request #238 from shehzan10/devel

Added warning messages for when submodules are not cloned
Merge pull request #239 from bkloppenborg/devel

Fix signed to unsigned comparison compiler warning.
BUG: Fixed issues with atan2 in CUDA and OpenCL backends

- This should fix issue #236
Merge pull request #240 from pavanky/atan2

BUG: Fixed issues with atan2 in CUDA and OpenCL backends
TEST: Adding global reduction tests
Changing af::af_cfloat to af::cfloat for C++ API
Properly catching and returning errors from af_sort*
TESTS: Adding tests for math functions