channel.c: WIP remove redundant method check and added FUNC_ATTR_NONNULL_ALL macro
channel.c channel_defs.h helpers.c: added Error field to RequestEvent, added no_op handler func
channel.c: use const char* instead of string and cleanup
channel.c; channel_defs.h; helpers.c: removed error from event again; send errors directly to the channel without using handlers and events
channel.c: fixed memory leak and lint errors
api/private/dispatch.c; api/vim.c; msgpack_rpc/channel.c msgpack_rpc/helpers.c added Error* field to msgpack_get_handler_for; further refactored channel.c
channel.c:323 changed order of evaluation in if statement
channel.c: removed superflous whitespace
dispatch.c: review comment
