v2.1.0

There are a few bug fixes/improvements in Kevin Heifner's fork of cpp-base64.
This release bumps up from 2.rc.7 to 2.rc.09 from the fork with the following changes:

• A bug fix allowing for unpadded strings
• Modified to be header-only
• Templated for various string / char containers
• Performance improvements (decoding via lookup table)
  • speed improvements measured at 4x-6x over v2.0.8

Thanks @boorad for the contribution #32