import of riakc_ppx project
fix riakc_ppx.3.1.0 url archive and checksum
Include omake as a dependency

Require ocaml version 4.02.0+ (kudos @yallop)
require ocaml 4.02.1, ppx_deriving_protobuf 2.0
Merge pull request #3133 from struktured/master

import of riakc_ppx project