Bug 69422

Equeue contains a generic implementation of queues of events of any type, and a 
specific implementation of queues of file descriptor events.

The generic module allows to associate an event queue with an event source, and 
one or several event handlers. The event source generates new events that are 
triggered from the outer world. The handlers consume events, but it is allowed 
that handlers also generate events.
The module for file descriptor events already defines an event source; this 
source watches registered file descriptors and produces events if a descriptor 
wants to deliver data, or if a descriptor is ready to accept data. As in the 
generic module, the handlers consume the events.

The concept of engines is suggested to construct event-driven programs in a 
systematic way. There are already a number of basic engines (polling, copying, 
connecting with a network service, accepting connections, SOCKS), and a number 
of operations for engines (sequential execution, synchronization).  

It is possible to let Equeue cooperate with the event queue implementation of 
Tcl.  Now, also the Shell library is included in the Equeue distribution.