Got rid of riak_index_entry

Used a tuple and a wrapper function (int -> string conversion) that
looks like a class.

Seeking comments.
Got rid of the wrapper function.
PEP8 fixes..

Just fixed the one that I encountered.
Got rid of apply func calls

Got rid of deprecated calls and used modern approach. Also fixed what
seems like a type in `RiakObject.reduce`, it should be `*args` rather
than just `param`
Merge pull request #192 from shuhaowu/use-func-call

Got rid of apply func calls
Merge pull request #191 from shuhaowu/no-index-entry

Got rid of riak_index_entry