Adding a time unit

1. Provide a conversion to picoseconds for use by TTime::SetPicoseconds and the TTime picoseconds constructor.
   Typically, you provide constants that define the number of picoseconds per unit and the number of units per second.
   
2. Provide a constructor that takes a const TTime& to support conversion between the TTime classes.
   Typically, you also provide a constructor that takes a number of time units.
   
3. Provide a function that returns the number of units an object represents.
   For example, the GetDays function of the TDays instance aWeek would return the number of days aWeek represents.
   

• Two constants that define the relationships between picoseconds and ticks and between seconds and ticks (kPicosecondsPerTick and kTicksPerSecond)

  const double TMIDITick::kPicosecondsPerTick= 1.E6;
  const double TMIDITick::kTicksPerSecond = 
      TTime::kPicosecondsToSeconds / TMIDITick::kPicosecondsPerTick;

• Constructors that take the number of ticks or any TTime object

  TMIDITick::TMIDITick( const TTime& time )
      :   TTime( time )
  { }
  
  TMIDITick::TMIDITick( TMIDITick::Tick ticks )
      :   TTime(TPicoseconds( ticks * kPicosecondsPerTick ))
  { }
  
  TMIDITick::TMIDITick( const TMIDITick& other )
      :   TTime( other )
  { }

• A function that returns the number of ticks represented by a TMIDITick object, TMIDITick::GetTicks

  TMIDITick::Tick TMIDITick::GetTicks() const
  {
      TMIDITick::Tick ticks = GetPicoseconds() / kPicosecondsPerTick;
      return ticks;
  }