Adding stateless delta decoding API

[codemerx]

Adds the stateless delta decoding API:

 static isDelta(payload: Buffer): bool
static applyDelta(current: Buffer, previous: Buffer): Buffer

[paddybyers]

These comments apply to both PRs that are here.

Please can we have a README that includes a description of the purpose of this library and an overview of the API and how it is used. I know that primarily we will be pointing developers at the Ably codec, but this library still needs to be usable in its own right.

Also, what are your plans for CI?

I think if possible we should construct a test and example app that doesn't use Ably. Do you have any thoughts about that?

[QuintinWillison]

@codemerx, is this branch now obsolete, replaced by that underlying #3?

If so could you please close this PR and delete the branch, albeit after ensuring you've done something to address @paddybyers's comment, even if that just means raising issues for the backlog.

Thanks.

[codemerx]

@codemerx, is this branch now obsolete, replaced by that underlying #3?

If so could you please close this PR and delete the branch, albeit after ensuring you've done something to address @paddybyers's comment, even if that just means raising issues for the backlog.

Thanks.

Yep this should be obsolete and it makes to sense to address teh comment. I am a bit hesitant to delete the branch, however, before the new structure gets final approval.