Decodes the string 's' from base64 encoding to plain text. The decoded string may contain the null byte (ie. hex 00). Otherwise, this is the same behaviour as the world.Base64Decode function. Bytes that are invalid are skipped (eg. spaces, newlines, other junk).
eg.
print (utils.base64decode ("TmljayBHYW1tb24=")) --> Nick Gammon
If the source string is not a multiple of 4 bytes then the last few bytes of the decoded string will be lost (because decoding is done in batches of 4 input bytes to 3 output bytes).