Mp3读取，Effect Remove

Signed-off-by: TRAfoer <lhf190@outlook.com>

Assets/NLayer/Decoder/LayerIDecoder.cs

@@ -0,0 +1,36 @@
+/*
+ * NLayer - A C# MPEG1/2/2.5 audio decoder
+ * 
+ */
+
+using System;
+
+namespace NLayer.Decoder
+{
+    // Layer I is really just a special case of Layer II...  1 granule, 4 allocation bits per subband, 1 scalefactor per active subband, no grouping
+    // That (of course) means we literally have no logic here
+    class LayerIDecoder : LayerIIDecoderBase
+    {
+        static internal bool GetCRC(MpegFrame frame, ref uint crc)
+        {
+            return LayerIIDecoderBase.GetCRC(frame, _rateTable, _allocLookupTable, false, ref crc);
+        }
+
+        // this is simple: all 32 subbands have a 4-bit allocations, and positive allocation values are {bits per sample} - 1
+        static readonly int[] _rateTable = { 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0 };
+
+        static readonly int[][] _allocLookupTable = { new int[] { 4, 0, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16 } };
+
+        internal LayerIDecoder() : base(_allocLookupTable, 1) { }
+
+        protected override int[] GetRateTable(IMpegFrame frame)
+        {
+            return _rateTable;
+        }
+
+        protected override void ReadScaleFactorSelection(IMpegFrame frame, int[][] scfsi, int channels)
+        {
+            // this is a no-op since the base logic uses "2" as the "has energy" marker
+        }
+    }
+}