rest-gen: Haskell: Escape reserved names
Rest-core: add Show instances for Header, Param and Dict.
Rest-core: add multi-DELETE handler.
Rest-gen: generate docs and code for multi-delete.
Rest-core: explicit exports and remove unused code.
Rest-core: don't put Cache-Control: private on files.

This way they can be cached by public proxies, e.g. cloudfront.
Bump rest-core and rest-gen.
Rest-core/rest-gen: Add changelog.
rest-types: Replace `StringMap [(a,b)]` with `StringMap (HashMap String a)`