change the default `UVX_LOGNODE_MAXBUF` to 1024 (from old 1000) bytes, for better memory alignment.
uvx log now supports serialize before send.

add `uvx_log_serialize`, `uvx_log_send_serialized`, and `UVX_LOG_SERIALIZE`, see uvx.h for more docs.
note in docs that only call `uvx_log_send()` in libuv's main loop thread. be limited by libuv.