add ps_fopen to properly handle fopen on Windows

fixes #22

src/fileutils.cpp

@@ -0,0 +1,12 @@
+#include "fileutils.h"
+#ifdef _WIN32
+#include "utfutils.h"
+#endif
+
+FILE* ps_fopen(const char* path, const char* mode) {
+#ifdef _WIN32
+  return _wfopen(utf8To16(path).c_str(),utf8To16(mode).c_str());
+#else
+  return fopen(path,mode);
+#endif
+}