[cosmo-dev] feed service spec updates

[Brian Moseley]

i've updated the feed service spec to describe changes we're making in
cosmo 0.10. specific feature changes include:

* create collection
* delete collection
* update collection now returns a 200 response with ETag and
Last-Modified headers and the updated representation (rather than a
204)

there are also some copy edits and clarifications.

<http://chandlerproject.org/bin/rdiff/Projects/CosmoFeedCollections?rev2=4&rev1=7&render=sidebyside>