Renamed three sequencetools functions.

OLD:

    sequencetools.get_sequence_elements_at_indices()
    sequencetools.increase_sequence_elements_at_indices_by_addenda()
    sequencetools.increase_sequence_elements_cyclically_by_addenda()

NEW:

    sequencetools.get_elements()
    sequencetools.increase_elements_at_indices()
    sequencetools.increase_elements_cyclically()

CHANGE: should be noted in the 2.15 change log.