Add implementation for immediate conflicts

Add implementation for immediate conflicts

Two events are said to be in immediate conflict
if they are conflicting but if the removal of
either event from their shared history would
result in a conflict-free set. That is, if
the only conflict among the set of events in
the history of the two events `e` and `e'`
is between `e` and `e'`, then `e` and `e'`
are in immediate conflict