Catalog Format v0

A specific format for catalog files is needed. v0 will consist of a Carbonado Catalog Header, plus some Postcard-encoded metadata, and then is suffixed with an unbounded series of Bao segment hashes, to be assembled by the node.

The extension for Carbonado Catalog files will be .cc, and Carbonado Catalog Indexes will be .cci. Indexes will be implemented separately, as defined in the issue #3.