Add ability to disable inlining of functions

Some build environments build each source file individually to .o files
and then link after the fact. With inlined functions, this tends to
just produce empty .o files, undefined symbol errors, and grumpy
programmers like me.

This change simply adds the option to disable inlining of functions so
Handmade Math can function properly as a library unto itself.

HandmadeMath.h

@@ -49,6 +49,22 @@
      #define HANDMADE_MATH_IMPLEMENTATION
      #define HANDMADE_MATH_NO_SSE
 
+  ==========================================================================
+
+  To disable inlining functions, you MUST
+
+  #define HANDMADE_MATH_NO_INLINE
+
+  in EXACTLY one C or C++ file that includes this header, BEFORE the
+  include, like this:
+
+     #define HANDMADE_MATH_IMPLEMENTATION
+     #define HANDMADE_MATH_CPP_MODE
+     #define HANDMADE_MATH_NO_INLINE
+     #include "HandmadeMath.h"
+
+  All other files should just #include "HandmadeMath.h" without the #define.
+
   Version History:
       0.2 (*) Updated documentation
           (*) Better C compliance
@@ -111,7 +127,9 @@ extern "C"
 #define HMMDEF extern
 #endif
 
-#if _MSC_VER && !__INTEL_COMPILER
+#ifdef HANDMADE_MATH_NO_INLINE
+#define HINLINE
+#elif _MSC_VER && !__INTEL_COMPILER
 #define HINLINE __inline
 #else
 #define HINLINE inline