Decode the Ascii85 encoded bytes-like object or ASCII string b.
foldspaces is a flag that specifies whether the 'y' short sequence
should be accepted as shorthand for 4 consecutive spaces (ASCII
0x20). This feature is not supported by the standard Ascii85
encoding used in PDF and PostScript.
adobe controls whether the <~ and ~> markers are present. While
the leading <~ is not required, the input must end with ~>, or a
ValueError is raised.
ignorechars should be a byte string containing characters to ignore from the
input. This should only contain whitespace characters, and by default
contains all whitespace characters in ASCII.
If canonical is true, non-canonical encodings are rejected.
The result is returned as a bytes object.