Add "mekacrc", not hooked up or validated

SabreTools.Hashing/Checksum/MekaCrc.cs

@@ -0,0 +1,46 @@
+using System;
+
+namespace SabreTools.Hashing.Checksum
+{
+    /// <see href="https://github.com/ocornut/meka/blob/master/meka/srcs/checksum.cpp"/> 
+    public class MekaCrc : ChecksumBase<ulong>
+    {
+        /// <inheritdoc/>
+        public override int HashSize => 64;
+
+        public MekaCrc()
+        {
+            Initialize();
+        }
+
+        /// <summary>
+        /// Reset the internal hashing state
+        /// </summary>
+        public override void Initialize()
+        {
+            _hash = 0;
+        }
+
+        /// <inheritdoc/>
+        /// <remarks>The original code limits the maximum processed size to 8KiB</remarks>
+        protected override void HashCore(byte[] data, int offset, int length)
+        {
+            // Read the current hash into a byte array
+            byte[] temp = BitConverter.GetBytes(_hash);
+
+            // Loop over the input and process
+            for (int i = 0; i < length; i++)
+            {
+                byte v = data[offset + i];
+                unchecked
+                {
+                    temp[v & 7]++;
+                    temp[v >> 5]++;
+                }
+            }
+
+            // Convert the hash back into a value
+            _hash = Convert.ToUInt64(temp);
+        }
+    }
+}