[webcomponents] Added a couple of algorithms and definitions. (#53)

Started fleshing things out in the proposal. @rniwa @annevk @hayatoito PTAL.
You can view, comment on, or merge this pull request online at:

  https://github.com/w3c/webcomponents/pull/53

-- Commit Summary --

  * Added a couple of algorithms and definitions.

-- File Changes --

    M proposals/Slots-Proposal.md (70)

-- Patch Links --

https://github.com/w3c/webcomponents/pull/53.patch
https://github.com/w3c/webcomponents/pull/53.diff

---
Reply to this email directly or view it on GitHub:
https://github.com/w3c/webcomponents/pull/53