[MERGE][RFC] Add simple revision serializer based on RIO.

[Ian Clatworthy]

Jelmer Vernooij wrote:
> Hi Ian,
> 
> Ian Clatworthy wrote:
>>  I'd like to see this patch
>> resubmitted so that this serialiser is used in a proposed new
>> development format.

> The attached patch adds "development7-rich-root" that is basically
> "development6-rich-root" that uses the RIO revision serializer.

Thanks!

> As I mentioned in my other mail, the main reason I think this change
> is needed is because we currently can't cope with some special
> characters in commit messages, revision properties or committer names
> as XML doesn't allow us to.

FWIW, I understood that and agree. With the emphasis on performance for
2.0 though, we need to benchmark the change before including it. I'll do
that benchmark today.

Assuming this pans out, I'd personally like to see a new development
format ship with 1.15 that has this and Aaron's nested-tree metadata.
But that decision rests with others (jam, lifeless, poolie). My goal
here is to ensure they have the necessary information to choose the best
path forward.

Ian C.