v2.0.0a9

Full Changelog: v2.0.0a8...v2.0.0a9

• Rewrite and remove bad when_any tests that could deadlock
• Updated README with a complete list of STLAB_ CMake options
• Added an option to run STLAB_ with the minimal default executor thread pool size for testing
• Corrected docs for invoke_waiting()
• Added equality comparison to move_only test model
• Corrected all usage of invoke_waiting()
• Attempted to use iwyu - minimal success
• Split out tuple_algorithm_test (it was included twice in futures and channels)
• Added STLAB_MINIMAL_TASK_POOL option for testing
• Changed STLAB_NO_STD_COROUTINE in config.hpp to STLAB_STD_COROUTINE() to avoid mistakes in usage.