[Yaml-core] Support for !binary

[Sam V. <sa...@vi...>]

Seems like this was never implemented as specified at 
http://yaml.org/type/binary.html

I needed this, so it's attached.  Along with a couple of extra types 
from http://yaml.org/type/ that I could implement quickly, but I haven't 
finished them all.

sorry for the extra dependancy on MIME::Base64, I decided not to try to 
make the old testchunks support conditional testing based on installed 
modules ... no doubt you support this with Test::Chunks, Ingy?

Sam.