Optimize inference and learning process using mirror connections.

[marty1885]

In the Bachelor project by Ali Kaan Sungar, Hierarchical Temporal Memory Software Agent section 5.4.3. He purposes that mirrored synapses (maintaining 2 sets of identical synapses but running in the opposite direction) are a major optimization. Allowing a vastly reduced computation requirement.

The same tech can be also used in Etaler to enhance the performance further. But maintaining 2 lists of synapses is complicated under Etaler's DOD/functional API.