Batteries user guide : BatBase64

`sig exception Invalid_char exception Invalid_table type encoding_table = char array type decoding_table = int array val str_encode : ?tbl:BatBase64.encoding_table -> string -> string val str_decode : ?tbl:BatBase64.decoding_table -> string -> string val encode : ?tbl:BatBase64.encoding_table -> 'a BatIO.output -> 'a BatIO.output val decode : ?tbl:BatBase64.decoding_table -> BatIO.input -> BatIO.input val make_decoding_table : BatBase64.encoding_table -> BatBase64.decoding_table end`