extend: FeedForwardTeacher - ability to backup state and rollback to previous
extend: Teacher - require implementing of backupParameters and rollback methods
extend: Teacher - backup network parameters before each epoch
modify: Input - move initialization to public method, to allow easy reinitializing
fix: Neuron - better threshold
extend: Neuron - give access to sum
new: TeacherController - adaptive learning rate controller
modify: XOR example - use TeacherController