Legic: rewrite reader to use xcorrelation and precise timing (#654)

* Legic: rewrite reader to use xcorrelation and precise timing
 - Even tough Legic tags transmit just AM, receiving using
   xcorrelation results in a significantly better signal
   quality.
 - Switching from bit bang to a hardware based ssc frees
   up CPU time for other tasks e.g. prng and demodulation
 - Having all times based on a fixed ts, results in perfect
   rwd-tag synchronization without magic +/- calculations.
* hi_read_tx: remove jerry-riged hysteresis based receiver
- This feature got obsolete by a x-correlation based receiver.
* Legic: adjusted sampling to new ssp clock speed
- Sampling is 4 times faster and pipeline daly reduced to 1/4.
 The new code samples each bit earyler to account for the
 shorter pipeline. That introduced bit errors by leeking the
 next bit into the current one.
* Legic: average 8 samples for better noise rejection.
* Update CHANGELOG.md

include/legic.h

@@ -0,0 +1,27 @@
+//-----------------------------------------------------------------------------
+// (c) 2016 Iceman
+//
+// This code is licensed to you under the terms of the GNU GPL, version 2 or,
+// at your option, any later version. See the LICENSE.txt file for the text of
+// the license.
+//-----------------------------------------------------------------------------
+// LEGIC type prototyping
+//-----------------------------------------------------------------------------
+
+#ifndef _LEGIC_H_
+#define _LEGIC_H_
+
+#include "common.h"
+
+//-----------------------------------------------------------------------------
+// LEGIC
+//-----------------------------------------------------------------------------
+typedef struct {
+	uint8_t uid[4];
+	uint32_t tagtype;
+	uint8_t cmdsize;
+	uint8_t addrsize;
+	uint16_t cardsize;	
+} legic_card_select_t;
+
+#endif // _LEGIC_H_