nits and changes towards minimum viable SRI up to section 3.4
nits and ripping out spec text for image,iframe,track etc.
ripping out what used to be section 4: Caching
SHA-1 is known-weak according to Wikipedia/NIST/Bruce Schneier. And we're killing it for CAs. Adding it to the spec.
change HTML resposne to JSON, because we don't do iframes for now
update CSP reference: pointing to 2 instead of 1.1
updating references: mime type confusion is a non-issue without caching, fetch 'process request end-of-file' was missing
no need for the 'Recommendations' section without caching
removing (Shared)Worker interfacing
Adding a note about future plans to support all subresources
Merge pull request #74 from mozfreddyb/minimal-viable-sri

SRI: towards minimum viable SRI