Merge branch 'maint'

Merge branch 'maint'

* maint:
  Fixing up fft and constellation plot to better handle zooming.
  Fixing zooming capabilities. Time axis does not track any longer due to what looks like a matplotlib bug that resets the xlims after the zoom occurs.
  Fixing up other plotting tools for data read errors.
  Using .min and .max on scipy arrays instead of min() max(); seems to be more portable.
  Fix how the end of a file is handled.
  PFB resampler: fix it this way to avoid the signed/unsigned warning.
  PFB resampler: fixes bug where filter could be looking past the number of inputs.