Revert "Remove duplicate nmhash.c and nmhash.h files"

This reverts commit 2d042fd.

Author: jvdp1

test/hash_functions/nmhash.c

@@ -0,0 +1,8 @@
+#include "nmhash.h"
+int32_t nmhash32_test ( const void * key, size_t len, uint32_t seed ) {
+  return NMHASH32 (key, (const size_t) len, seed);
+}
+
+int32_t nmhash32x_test ( const void * key, size_t len, uint32_t seed ) {
+  return NMHASH32X (key, (const size_t) len, seed);
+}