Migrate recent HLLib work to BOS

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

BurnOutSharp.Models/VBSP/Header.cs

@@ -0,0 +1,31 @@
+namespace BurnOutSharp.Models.VBSP
+{
+    /// <see href="https://github.com/RavuAlHemio/hllib/blob/master/HLLib/VBSPFile.h"/>
+    public sealed class Header
+    {
+        /// <summary>
+        /// BSP file signature.
+        /// </summary>
+        public string Signature;
+
+        /// <summary>
+        /// BSP file version.
+        /// </summary>
+        /// <remarks>
+        /// 19-20:			Source
+        /// 21:				Source - The lump version property was moved to the start of the struct.
+        /// 0x00040014:		Dark Messiah - Looks like the 32 bit version has been split into two 16 bit fields.
+        /// </remarks>
+        public int Version;
+
+        /// <summary>
+        /// Lumps.
+        /// </summary>
+        public Lump[] Lumps;
+
+        /// <summary>
+        /// The map's revision (iteration, version) number.
+        /// </summary>
+        public int MapRevision;
+    }
+}