sandbox/mskmodem_test: fixing integration but for square pulses
sandbox/mskmodem_test: fixing integration but for square pulses

  * using trapezoidal integrator for phase accumulation
  * fixing half-sample timing offset with pulse shape
  * does not work for square pulses due to abrupt transition

JayKickliter/liquid-dsp,wangning223/liquid-dsp,cjcliffe/liquid-dsp,biotrump/liquid-dsp,JayKickliter/liquid-dsp,andrepuschmann/liquid-dsp,jgaeddert/liquid-dsp,wangning223/liquid-dsp,andrepuschmann/liquid-dsp,jgaeddert/liquid-dsp,jgaeddert/liquid-dsp,andrepuschmann/liquid-dsp,andrepuschmann/liquid-dsp,wangning223/liquid-dsp,biotrump/liquid-dsp,biotrump/liquid-dsp,biotrump/liquid-dsp,JayKickliter/liquid-dsp,cjcliffe/liquid-dsp,jgaeddert/liquid-dsp,biotrump/liquid-dsp,JayKickliter/liquid-dsp,wangning223/liquid-dsp,andrepuschmann/liquid-dsp,cjcliffe/liquid-dsp,cjcliffe/liquid-dsp,JayKickliter/liquid-dsp,wangning223/liquid-dsp,cjcliffe/liquid-dsp,jgaeddert/liquid-dsp