riak erlanl client search 新特性

新特性，返回结果：可以指定需要的列，并返回记录数。
Current behavior:
riakc_pb_socket:search(Pid, <<"phrases_custom">>, <<"phrase:fox">>).                
{ok,[[<<"phrases_custom">>,<<"5">>],
     [<<"phrases_custom">>,<<"1">>]]}

Proposed behavior:
riakc_pb_socket:search(Pid, <<"phrases_custom">>, <<"phrase:fox">>).
{ok,[{<<"phrases_custom">>,
        [{<<"id">>,<<"1">>}, 
         {<<"phrase">>,<<"The quick brown fox jumps over the lazy dog">>}],
     {<<"phrases_custom">>,
        [{<<"id">>,<<"5">>},
        {<<"phrase">>,<<"The quick brown fox jumps over the lazy dog">>}],
    0.0,2}
    %% Note the last two fields of the result are Max Score and Number Found.

Semi-compatible behavior by specifying the fl (with the exception of max score and number found):
riakc_pb_socket:search(Pid, <<"phrases_custom">>, <<"phrase:fox">>, [{fl,[<<"id">>]}], 5000, 5000).
{ok,[{<<"phrases_custom">>,[{<<"id">>,<<"1">>}]},
     {<<"phrases_custom">>,[{<<"id">>,<<"5">>}]},
    0.0,2}

(ejabberd@meta)47> riakc_pb_socket:search(Pid, <<"user2">>, list_to_binary("\"name\":6YOO546w*")).
{ok,{search_results,[{<<"user2">>,
                      [{<<"id">>,<<"jason">>},
                       {<<"name">>,<<"6YOO546w5peg">>},
                       {<<"sex">>,<<"male">>}]}],
                    0.0,1}}
(ejabberd@meta)48> riakc_pb_socket:search(Pid, <<"user2">>, list_to_binary("\"name\":6YOO546w*"),[{fl,[<<"id">>]}]).
{ok,{search_results,[{<<"user2">>,[{<<"id">>,<<"jason">>}]}],
                    0.0,1}}
(ejabberd@meta)49> riakc_pb_socket:search(Pid, <<"user2">>, list_to_binary("\"name\":6YOO546w*"),[{fl,[<<"id">>,<<"name">>]}]).
{ok,{search_results,[{<<"user2">>,
                      [{<<"id">>,<<"jason">>},{<<"name">>,<<"6YOO546w5peg">>}]}],
                    0.0,1}}
(ejabberd@meta)50>