src, deps: move string_search.h to nbytes, add version metadata

Author: jasnell

deps/nbytes/README.md

@@ -0,0 +1,5 @@
+# Node.js bytes (nbytes) library
+
+The `nbytes` library extracts certain Node.js specific byte manipulation
+functions from the core of Node.js itself and makes them available for
+use in other projects that need to emulate Node.js' behavior.