code: function interpolatePairs( _ps, t1, t2 ) {
    var pn = [];
    for (var i=0; i<_ps.length; i++) {
      var next = (i==_ps.length-1) ? 0 : i+1;
      pn.push( new Pair( _ps[i].interpolate( t1 ) ).to( _ps[next].interpolate( 1-t2 ) ) );
    }
    return pn;
  }
docs: create a list of interpolated pairs from a list of original pairs