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).
FIX -Wconversion warnings for src/nvim/cursor_shape.c
add -Wconversion flag to src/nvim/cursor_shape.c
FIX -Wconversion warnings on src/nvim/os/channel.c
add -Wconversion flag for src/nvim/os/channel.c
remove duplicated map.c from src/nvim/CMakeLists.txt
TRIVIAL: fix trailing blanks in src/nvim/eval.c
FIX -Wconversion warnings in src/nvim/os/fs.c
add -Wconversion flag for src/nvim/os/fs.c
sort files in alphabetical order, for better reading
FIX -Wconversion warnings for src/nvim/os/input.c
add -Wconversion flag for src/nvim/os/input.c