RFC 4648. It adds no line feed when encoding, and raise ArgumentError
if the encoded string contains non-alphabet (including CR and LF).
* lib/base64.rb: added. This provides encoding/decoding method for
Base64 in standard RFC 2045, Base64 in standard RFC 4648 and ``Base 64
Encoding with URL and Filename SafeAlphabet'' in RFC 4648.
* test_pack.c, test/base64/test_base64.rb: add tests for above.
git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@19553 b2dd03c8-39d4-4d8f-98ff-823fe69b080e
