330 WIP on redesigning the P25 C4FM decoder. Creates a new decoder

based on the P25 LSM decoder using a costas loop and a gardner detector.
Updates the Demodulator Viewer FX application to add in a symbol chart
and a phase error chart.  The decoder won't lock on yet ... still a wip.

src/main/java/io/github/dsheirer/dsp/psk/QPSKSymbolDecoder.java

@@ -0,0 +1,90 @@
+/*******************************************************************************
+ * sdr-trunk
+ * Copyright (C) 2014-2018 Dennis Sheirer
+ *
+ * This program is free software: you can redistribute it and/or modify it under the terms of the GNU General Public
+ * License as published by  the Free Software Foundation, either version 3 of the License, or  (at your option) any
+ * later version.
+ *
+ * This program is distributed in the hope that it will be useful,  but WITHOUT ANY WARRANTY; without even the implied
+ * warranty of  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License  along with this program.
+ * If not, see <http://www.gnu.org/licenses/>
+ *
+ ******************************************************************************/
+package io.github.dsheirer.dsp.psk;
+
+import io.github.dsheirer.dsp.symbol.Dibit;
+import io.github.dsheirer.sample.Broadcaster;
+import io.github.dsheirer.sample.Listener;
+import io.github.dsheirer.sample.complex.Complex;
+
+public class QPSKSymbolDecoder implements Listener<Complex>, IQPSKSymbolDecoder
+{
+	private Broadcaster<Dibit> mBroadcaster = new Broadcaster<Dibit>();
+	
+	/**
+	 * Slices a ComplexSample representing a phase shifted symbol according to
+	 * the following constellation pattern:
+	 * 
+	 *    \ 00 /
+	 *     \  /
+	 *   01 \/ 10
+	 *      /\
+	 *     /  \
+	 *    / 11 \
+	 */
+	public QPSKSymbolDecoder()
+	{
+	}
+	
+	public void dispose()
+	{
+		mBroadcaster.dispose();
+		mBroadcaster = null;
+	}
+
+	public void addListener( Listener<Dibit> listener )
+	{
+		mBroadcaster.addListener( listener );
+	}
+
+	public void removeListener( Listener<Dibit> listener )
+	{
+		mBroadcaster.removeListener( listener );
+	}
+
+	@Override
+	public void receive( Complex complex )
+	{
+		mBroadcaster.broadcast( decode( complex ) );
+	}
+	
+	public Dibit decode(Complex complex )
+	{
+		if( Math.abs( complex.inphase() ) > Math.abs( complex.quadrature() ) )
+		{
+			if( complex.inphase() > 0 )
+			{
+				return Dibit.D10_MINUS_1;
+			}
+			else
+			{
+				return Dibit.D01_PLUS_3;
+			}
+		}
+		else
+		{
+			if( complex.quadrature() > 0 )
+			{
+				return Dibit.D00_PLUS_1;
+			}
+			else
+			{
+				return Dibit.D11_MINUS_3;
+			}
+		}
+	}
+	
+}