MsgPack-RPC dispatch based on function array lookup #864

This simplifies the generated msgpack_rpc_dispatch() function, separates the
code for each RPC method more clearly and allows easy implementation of
alternative dispatching methods (e.g. string method id dispatch).
cmake: upgrade libuv 0.11.23 -> 0.11.26 #911

Fixes some bugs and increase the performance of uv_hrtime() on OSX, which
reduces its prominence in performance traces. This allows us to better see
what's really causing slowness.

ref:
- https://github.com/neovim/neovim/issues/868
- https://github.com/joyent/libuv/pull/1325
- https://github.com/joyent/libuv/releases