Jsont.Object.Mems.map make encoding and decoding optional. Like in overy other map.Jsont.Array.map make encoding and decoding optional. Like in every other map.Jsont_bytesrw.encode change the default buffer size to match the one hinted by the writer rather than Bytesrw.Bytes.Slice.io_buffer_size.jsont.{bytesrw,brr} export all requires.jsont tool remove spurious dependency on b0.std (#2).