[Rd] Adding support for S7 to base R

[Tomasz Kalinowski]

Dear R-devel,

We are pleased to inform you that the R Consortium OOP Working Group
has been making progress on the S7 (formerly named R7) package and are
preparing to submit it to CRAN. The S7 package is a new OOP system
designed to be a successor to S3 and S4.

As part of that effort, the group has identified a minimal set of
narrow changes to base R that would allow S7 to exist as a CRAN
package. The changes, in general, enable S7 to use R language features
that are presently limited to only S4.

The proposed patches:

-  make `@` an S3 generic.
-  make `%*%` an S3 generic.
-  enable double dispatch for S7.
-  enable `inherits()` to accept `S7_class` objects.

The diffs for the individual patches can be found here:

%*%      - https://github.com/r-devel/r-svn/pull/105.diff
inherits - https://github.com/r-devel/r-svn/pull/106.diff
Ops      - https://github.com/r-devel/r-svn/pull/107.diff
@        - https://github.com/r-devel/r-svn/pull/108.diff

The repository for the S7 package can be found here:
https://github.com/RConsortium/OOP-WG

Your feedback is important to us, and we would be grateful for your
input on these patches. We aim to ensure that S7 is a high-quality
package that benefits the R community, while being mindful of not
disrupting existing projects or introducing breaking changes. If you
have any concerns or objections, please let us know. Your insights and
suggestions will be instrumental in shaping the final version of these
patches, and we appreciate your help in this process.

Thank you for your attention and contributions.

Best regards,
Tomasz
On behalf of the R Consortium OOP Working Group