Portable thread pool

pthreadpool is a portable and efficient thread pool implementation. It provides similar functionality to #pragma omp parallel for, but with additional features. Features: * C interface (C++-compatible). * 1D-6D loops with step parameters. * Run on user-specified or auto-detected number of threads. * Work-stealing scheduling for efficient work balancing. * Wait-free synchronization of work items. * Compatible with Linux (including Android), macOS, iOS, Windows, Emscripten environments. * 100% unit tests coverage. * Throughput and latency microbenchmarks.