Fix ruby document

1. Organize collapsed ruby yard doc.

2. Update contents about ClientStub#bidi_streamer because
bidi#writes_done hasn't existed.

https://github.com/grpc/grpc/pull/14535#discussion_r171452923

3. Fix yardoc warnings.

Warings:

[warn]: Invalid tag format for @return in file `lib/grpc/core/time_consts.rb` near line 36
[warn]: @param tag has duplicate parameter name: set_input_stream_done
    in file `lib/grpc/generic/bidi_call.rb' near line 70
[warn]: Unknown tag @result in file `lib/grpc/generic/rpc_server.rb` near line 287
[warn]: @param tag has unknown parameter name:
    in file `lib/grpc/generic/interceptors.rb' near line 158
[warn]: In file `lib/grpc/generic/rpc_server.rb':217: Cannot resolve link to key: from text:
        ...{key: val, ..}
[warn]: In file `lib/grpc/generic/rpc_server.rb':217:
Cannot resolve link to key: from text:
        ...{key: val, ..}

0 files changed, 0 insertions, 0 deletions