MemoryBlock abstraction

Initial work by @nattthebear

Author: YoshiRulz

BizHawk.Common/BizHawk.Common.csproj

@@ -64,6 +64,8 @@
     <Compile Include="BizInvoke\CallingConventionAdapter.cs" />
     <Compile Include="BizInvoke\DynamicLibraryImportResolver.cs" />
     <Compile Include="BizInvoke\MemoryBlock.cs" />
+    <Compile Include="BizInvoke\MemoryBlockUnix.cs" />
+    <Compile Include="BizInvoke\MemoryBlockWin32.cs" />
     <Compile Include="BizInvoke\WaterboxUtils.cs" />
     <Compile Include="Buffer.cs" />
     <Compile Include="Colors.cs" />

BizHawk.Common/BizInvoke/CallingConventionAdapter.cs

@@ -140,7 +140,7 @@ static SysVHostMsGuest()
 			public SysVHostMsGuest()
 			{
 				int size = 4 * 1024 * 1024;
-				_memory = new MemoryBlock((ulong)size);
+				_memory = MemoryBlock.PlatformConstructor((ulong) size);
 				_memory.Activate();
 				_refs = new WeakReference[size / BlockSize];
 			}