[RFC][BBC] New revision serializer

[Andrew Bennetts]

Aaron Bentley wrote:
[...]
> Can't really agree there.  It's very similar to JSON in storage
> capability, but isn't human-readable.  It's used in bundles, for
> example.  It lacks support for unicode, tuples and sets, which can
> sometimes be a pain, though.

(Btw, our bencode.py now has a bdecode_as_tuple function, which produces tuples
rather than lists, which is considerably more convenient than turning nested
lists into nested tuples after the fact.)

-Andrew.