feat: add Math library source and integrate into MSVC project and VM initialization

Add wren_math.c and wren_math.h to the MSVC 2013 project files, including both the .vcxproj and .vcxproj.filters. Also fix the indentation of the WREN_COMPUTED_GOTO comment in wren_common.h and correct a conditional guard bug in wren_vm.c where wrenLoadMathLibrary was guarded by WREN_USE_LIB_IO instead of WREN_USE_LIB_MATH.

src/wren_common.h

@@ -30,7 +30,7 @@
 // Defaults to on.
 #ifndef WREN_COMPUTED_GOTO
   #ifdef _MSC_VER
-  // No computed gotos in Visual Studio.
+    // No computed gotos in Visual Studio.
     #define WREN_COMPUTED_GOTO 0
   #else
     #define WREN_COMPUTED_GOTO 1

src/wren_vm.c

@@ -7,6 +7,9 @@
 #if WREN_USE_LIB_IO
   #include "wren_io.h"
 #endif
+#if WREN_USE_LIB_MATH
+  #include "wren_math.h"
+#endif
 
 #include <stdlib.h>
 #include <stdio.h>
@@ -72,6 +75,9 @@ WrenVM* wrenNewVM(WrenConfiguration* configuration)
   #if WREN_USE_LIB_IO
     wrenLoadIOLibrary(vm);
   #endif
+  #if WREN_USE_LIB_IO
+    wrenLoadMathLibrary(vm);
+  #endif
 
   return vm;
 }