FIX: OSX disable app-nap during serial comm (@anticat)

https://github.com/Proxmark/proxmark3/pull/687

client/util_darwin.h

@@ -0,0 +1,17 @@
+//-----------------------------------------------------------------------------
+// (c) 2018 AntiCat
+//
+// This code is licensed to you under the terms of the GNU GPL, version 2 or,
+// at your option, any later version. See the LICENSE.txt file for the text of
+// the license.
+//-----------------------------------------------------------------------------
+// macOS framework bindings
+//-----------------------------------------------------------------------------
+
+#ifndef UTIL_DARWIN_H__
+#define UTIL_DARWIN_H__
+
+void disableAppNap(const char* reason);
+void enableAppNap();
+
+#endif