use fold for merkle tree generation
use fold for merkle tree generation

amyvmiwei/riak,basho/riak_search,authbox-lib/riak,xuejianhai/riak_search,elkingtonmcb/riak,biddyweb/riak,xuejianhai/riak_search,basho/riak,planobe/riak,yangchengjian/riak,xuejianhai/riak,laurenrother/riak,DavidAlphaFox/riak,wwezhuimeng/riak_search,basho/riak_search,planobe/riak,GabrielNicolasAvellaneda/riak,glickbot/riak,wwezhuimeng/riak_search