src: replace naive search in Buffer::IndexOf

Adds the string search implementation from v8
which uses naive search if pattern length < 8
or to a specific badness then uses Boyer-Moore-Horspool

Added benchmark shows the expected improvements
Added option to use ucs2 encoding with Buffer::IndexOf

Reviewed-By: James M Snell <jasnell@gmail.com>
Reviewed-By: Trevor Norris <trev.norris@gmail.com>
PR-URL: https://github.com/nodejs/node/pull/2539