added `Thread` class, corrections, additional tests and libuv examples

• threading feature requires PHP ZTS, and not fully working.
• thread tests working most part, some works on Windows, segmentation on Linux, they are skipped for now.
• uv_queue_work is used to the mimic missing uv_thread_* features from libuv extension ext-uv .
• added additional libuv only examples showing actual execution flow among each other handles.
• added staging Channels class for threads, but not working the same way as Spawn/Parallel, needs a lot of work, mostly likely not even possible.
• various other corrections.