Base64 user-facing docs should say that decode can handle URL Safe encoding

Base64 has static methods specific to doing URLSafe encoding, but has no corresponding URLSafe decoding method.

This is be cause the decoding table transparently handles both URLSafe and standard alphabets. Unfortunately this is only documented as a javadoc on a private member.

There should be a mention of it

• In the class javadocs
• on the static decode methods
• on the static URLSafe encode methods