Add pattern generator output

[joschaschmiedt]

See Roberto Fasano's labyak for an example that uses streaming for pattern generation such as

  period=4.5e-3
  sequence = {3: [(0, 1),         # start high
                  (1e-3, 0),      # switch to low at 1 ms
                  (1.5e-3, 1),    # switch to high at 1.5 ms
                  (3.5e-3, 0)]}   # switch to low at 3.5 ms

  labjack.pattern.start(sequence, period)