chosing latest MIME::Base64

MIME::Base64's latest version on CPAN is 3.13, which fixes the encode_base64url() behaviour.
updated 'progress' content on README

Data generated by cover.sh on Feb 1st, 2013
Merge pull request #172 from garu/patch-2

updated 'progress' content on README
Merge pull request #171 from garu/patch-1

chosing latest MIME::Base64