firpfbch/sandbox: adding forward declaration of internal methods
firpfbch/sandbox: adding forward declaration of internal methods

  * sandbox is for testing pruposes so internal methods are not globally
    defined
  * adding forward declaration rids compiler of annoying warnings
  * helps clean up build process

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