Base64

`sig exception Invalid_char exception Invalid_table type encoding_table = char array type decoding_table = int array val str_encode : ?tbl:Base64.encoding_table -> string -> ExtBytes.Bytes.t val str_decode : ?tbl:Base64.decoding_table -> ExtBytes.Bytes.t -> string val encode : ?tbl:Base64.encoding_table -> 'a IO.output -> 'a IO.output val decode : ?tbl:Base64.decoding_table -> IO.input -> IO.input val make_decoding_table : Base64.encoding_table -> Base64.decoding_table end`