- Add platform helpers for pipe creation.
- Change the direct-to-fds implementation to create a wsi for each
pt and use the normal apis to bind it to the event loop.
- Modifiy context creation and destroy to create and remove the
event pipe wsis.
- Create the event pipe wsis during context create if using the
default poll() event loop, or when the other event loops start
otherwise.
- Add handler that calls back user code with
LWS_CALLBACK_EVENT_WAIT_CANCELLED
This patch allows you to call `lws_cancel_service(struct lws_context *context)`
from another thread.
It's very cheap for the other thread to call and is safe without
locking.
Every use protocol receives a LWS_CALLBACK_EVENT_WAIT_CANCELLED from
the main thread serialized normally in the event loop.
