Add win32 ffi example.

CHANGELOG.md

@@ -2,6 +2,7 @@
 All notable changes to this project will be documented in this file.
 
 ## 1.23.1 - ???
+- Add FFI support to 64-bit windows compiled with MSVC
 - Don't process shared object names passed to dlopen.
 - Add better support for windows console in the default shell.c for autocompletion and
   other shell-like input features.

examples/ffi/win32.janet

@@ -0,0 +1,7 @@
+(ffi/context "user32.dll")
+
+(ffi/defbind MessageBoxA :int
+  [w :ptr text :string cap :string typ :int])
+
+(MessageBoxA nil "Hello, World!" "Test" 0)
+