module Base64:Base64 codec.sig..end
8-bit characters are encoded into 6-bit ones using ASCII characters A-Z,
a-z, 0-9, and '+' , '/' (in that order).
exception Invalid_char
val str_encode : string -> stringval str_decode : string -> stringInvalid_char if a
character in the input string is not a valid one.val encode : 'a IO.output -> 'a IO.outputval decode : IO.input -> IO.input