charm: add BundleData, parser and Verify method.

This is the start of the bundle specification discussed at https://docs.google.com/document/d/1SF8hTBi6oVbki8V__beNij6wnQU-5cm6PZsy5gf0j_Y
Existing bundles will not work - this format is not backwardly compatible, because
it defines everything at the top level, rather than having a "basket" of bundles.

If need be, we could write a tool to do the conversion.