core: framework for creating asynchronous pool of workers

- dedicated group of processes that can get tasks from other processes
  via memory pipe
- react immediately, no time based polling
- should reduce the need for other components to create extra processes
  for special handling
async: new function async_task_route(rname)

- execute actions in a routing block via core async framework
core: async_workers - new core parameter

- specify how many processes to create for asyn framework
- default is 0 (asyn framework disabled)
- you must set it to >0 to enable it
async: documentation for async_task_route()
async: fixed type in the title of async_route() example