- fixed issue of second stop bit required
- implemented a new serial protocol (binary):
  [0000xxxx 0001xxxx] 0010xxxx 0011xxxx 0100xxxx 0101xxxx 0110xxxx 0111xxxx
  The most significant nibble contains the address, the least significant nibble contains the data
  address 0000: pwm period, most significant nibble
  address 0001: pwm period, least significant nibble
  address 0010: pwm red, most significant nibble
  address 0011: pwm red, least significant nibble
  address 0100: pwm green, most significant nibble
  address 0101: pwm green, least significant nibble
  address 0110: pwm blue, most significant nibble
  address 0111: pwm blue, least significant nibble
  The pwm period is optional.