Add specifications and EDoc comments to exported functions

[Tronso]

There are many exported functions in riak_core_lite without function specifications or EDoc comments. Some functions are commented on but the comments are missing the edoc tags. According to the edoc documentation it is also preferable to use the standard Erlang -spec specifications instead of the EDoc @spec comments, which can be found in the code.

Checklist of modules to track progress:

• [x] chash.erl
• [x] chashbin.erl
• [x] gen_nb_server.erl
• [ ] riak_core.app.src
• [x] riak_core.erl
• [x] riak_core_apl.erl
• [x] riak_core_app.erl
• [x] riak_core_claim.erl
• [x] riak_core_claimant.erl
• [ ] riak_core_claim_util.erl
• [ ] riak_core_eventhandler_guard.erl
• [ ] riak_core_eventhandler_sup.erl
• [ ] riak_core_gossip.erl
• [x] riak_core_handoff_listener.erl
• [x] riak_core_handoff_listener_sup.erl
• [x] riak_core_handoff_manager.erl
• [x] riak_core_handoff_receiver.erl
• [x] riak_core_handoff_receiver_sup.erl
• [x] riak_core_handoff_sender.erl
• [x] riak_core_handoff_sender_sup.erl
• [x] riak_core_handoff_sup.erl
• [ ] riak_core_node_watcher.erl
• [ ] riak_core_node_watcher_events.erl
• [ ] riak_core_priority_queue.erl
• [x] riak_core_ring.erl
• [ ] riak_core_ring_events.erl
• [ ] riak_core_ring_handler.erl
• [x] riak_core_ring_manager.erl
• [ ] riak_core_ring_util.erl
• [ ] riak_core_send_msg.erl
• [ ] riak_core_status.erl
• [ ] riak_core_sup.erl
• [ ] riak_core_test_util.erl
• [ ] riak_core_util.erl
• [x] riak_core_vnode.erl
• [ ] riak_core_vnode_manager.erl
• [ ] riak_core_vnode_master.erl
• [ ] riak_core_vnode_proxy.erl
• [ ] riak_core_vnode_proxy_sup.erl
• [ ] riak_core_vnode_sup.erl
• [ ] riak_core_vnode_worker.erl
• [ ] riak_core_vnode_worker_pool.erl
• [ ] vclock.erl

[Tronso]

To prevent errors in the specification blocking the master pipeline the issue is handled on branch 78_documentation.