A Qt5 based GUI demonstration of the various filtering capabilities of the spuce library

This was originally for SPUC library and is now largely redundant since the spuce library self contains various QT apps. However, it does show as a standalone example how to use the spuce library

This uses

QCustomPlot library (www.qcustomplot.com) - GPL v3

Requirements:

	cmake
	qt5
	spuce

	(see .travis.yml or .travis.linux for install steps if needed)
	cd build
	cmake ..
	make

Use the mouse to select cut-off, etc

Simulataneously enable multiple filters for comparison

Filter types in SPUCE (not all in this app):

   * Butterworth
   * Chebyshev
   * Elliptic
   * Maximally flat FIR
   * Remez Equiripple
   * Raised Cosine FIR
   * Gaussian FIR
   * CIC
   * Notch filter
   * Cut/Boost Filter
   * Halfband/Subband IIR filters