Proposal idea: consensus diffs might make microdescs obsolete?

When we introduced microdescriptors, the only reason we made them a separate set of documents was that they changed less frequently than the consensus. But with support for consensus diffs [(or maybe something even better)][#343] it's not clear that logic still applies. It might be better instead to just have the standard document be a consensus with all the microdesc info built in, and then just get a diff from each of those to the next one.

I'm putting this in Icebox since we're all busy right now, and since there's an outside chance we go and build walking onions before we ever get to this.