* added (very wip) llvm_compute class which currently generates cuda/nvidia ptx code and opencl spir code from c++ code (c++14 + gnu/clang extensions) using a modified clang/llvm/libc++ 3.5
 * the llvm_compute class can also load ptx code and generate actual device binaries using the functionality provided by the cuda low-level api and jit compiler (cuModuleLoadDataEx etc.)
 * moved cuda exception/error handling to the opencl.hpp header (where cudacl is defined) so that it can be used externally (+added static cuda_error_code_to_string function + misc getters)
 * updated build and install script and xcode project (new compute folder)