examples/tt_proto.erl doc doesn't build right

`./rebar doc` doesn't seem to pick up the examples docs. For now, `doc/tt_proto.md` was built manually by going into the `examples/` directory and calling `edoc:file("tt_proto.erl",[{layout,edown_layout},{file_suffix,".md"}])` and then copying the `tt_proto.md` file to `doc/`.
