Add BitWordModulator

Justification:
- BitWordModulator supposed to be different (faster) implementation
  of modulator and will be used instead of Modulator/ModulatorImpl.
  However, at the moment it is the exact copy of ModulatorImpl,
  neglecting the inheritance from Modulator
Update BitWordModulator

Details:
- add basic modulation/demodulation based on BitWords
Too sleepy to write any decent comment
Merge branch 'bitword.implementation' into develop