Spin-off remaining linked documentation work from DROOLS-1272 for:
Include docs on state machine and thread safety
Ensure the N&N section describing state machine and thread-safety is correctly reflected in section of the manual.

[From sterobin@redhat.com]
Confirmed with Mark and Mario that the state machine diagram does not belong in the docs, at least for now. Note from Mark in chat: "all they need to know is 1) there three interacting threads: user, timer and engine 2) we have a state machine based algorithm to efficient co-ordinate those threads and ensure thread safety."

Attached the state machine diagrams from Mark for future ref, if needed.