Encode bytes-like object b using Ascii85 and return a bytes object.
foldspaces is an optional flag that uses the special short sequence 'y'
instead of 4 consecutive spaces (ASCII 0x20) as supported by 'btoa'. This
feature is not supported by the standard encoding used in PDF.
If wrapcol is non-zero, insert a newline (b'\n') character after at most
every wrapcol characters.
pad controls whether zero-padding applied to the end of the input
is fully retained in the output encoding, as done by btoa,
producing an exact multiple of 5 bytes of output.
adobe controls whether the encoded byte sequence is framed with <~
and ~>, as in a PostScript base-85 string literal. Note that
while ASCII85Decode streams in PDF documents must be terminated
with ~>, they must not use a leading <~.