Add ring buffer edge IPC.

This patch adds a ring buffer IPC to implement very fast data
passing between nodes within the same address space (same process).
The ring buffer can be used effectively to pass a primative type
value (e.g., int or pointer) or struct between producer and consumer.

There are restrictions:
1) Producer and consumer must be within the same process.
2) The same amount of data must be produced and consumed each
   node invocation. That is, a producer cannot write 4 bytes
   one invocation and then 8 bytes the next.

TODO: Support ring buffer IPC on shared memory (allow producer
   and consumer to be in different processes).