Migrate recent HLLib work to BOS

It's better suited for the model of BOS and not an update to HLLibSharp

BurnOutSharp.Models/GCF/DataBlockHeader.cs

@@ -0,0 +1,36 @@
+namespace BurnOutSharp.Models.GCF
+{
+    /// <see href="https://github.com/RavuAlHemio/hllib/blob/master/HLLib/GCFFile.h"/>
+    public sealed class DataBlockHeader
+    {
+        /// <summary>
+        /// GCF file version.  This field is not part of all file versions.
+        /// </summary>
+        public uint LastVersionPlayed;
+
+        /// <summary>
+        /// Number of data blocks.
+        /// </summary>
+        public uint BlockCount;
+
+        /// <summary>
+        /// Size of each data block in bytes.
+        /// </summary>
+        public uint BlockSize;
+
+        /// <summary>
+        /// Offset to first data block.
+        /// </summary>
+        public uint FirstBlockOffset;
+
+        /// <summary>
+        /// Number of data blocks that contain data.
+        /// </summary>
+        public uint BlocksUsed;
+
+        /// <summary>
+        /// Header checksum.
+        /// </summary>
+        public uint Checksum;
+    }
+}