Perl version of Python's URL-safe base64 codec

 MIME::Base64::URLSafe is a perl version of python's URL-safe base64 encoder /
 decoder.
 .
 When embedding binary data in URL, it is preferable to use base64 encoding.
 However, two characters ('+' and '/') used in the standard base64 encoding have
 special meanings in URLs, often leading to re-encoding with URL-encoding, or
 worse, interoperability problems.
 .
 To overcome the problem, the module provides a variation of base64 codec
 compatible with python's urlsafe_b64encode / urlsafe_b64decode