Digest wrap up: validators, algorithm parameters and buggy compression

Hi @all,

during today's meeting we pointed three main issues on which we need the
community support.
Probably once we close the two issues below the spec will be ready for a
call.

## Cache & Validators

RFC3230 spec says:

>The resource is specified by the effective request URI
>and any cache-validator contained in the message.

Can we just say that

>`Validators` like `Last-Modified` and `ETag`
>or other caching header fields
>may indicate the freshness of the conveyed representation.

In which way `validators` specify a resource?
Should we remove the `specify` term?

## Algoritm parameters

RFC3230 says that digest-algorthms can have parameters.
Probably we have just two possibilities: which is the better one?
We can even *pick* the one we like the most as long as this spec OBSOLETES
RFC3230.

1) Digest: mi-sha256=dcRDgR2GM35DluAV13PzgnG6+pvQwPywfFvAu1UeFrs=; rs=40

2) Digest: mi-sha256;rs=40=dcRDgR2GM35DluAV13PzgnG6+pvQwPywfFvAu1UeFrs=


## Buggy compression

While we need community feedback on the above points, I wanted to
answer to Watson question hoping that this thread won't hijack the
community attention :)

Watson asked how to use Digest for protecting from buggy compression, and
his question deserves at least a FAQ or a consideration in the spec, so I
filed https://github.com/httpwg/http-extensions/issues/1208

Thanks for all your time,
R.