Add WaiSubsiteWithAuth

[mchaver]

This newtype and instances will allow the WaiSubsite to pick up isAuthorized from the parent site. I followed the code for Static subsites. I am guessing it makes sense to have both WaiSubsite and WaiSubsiteWithAuth because it is possible that we want to have a WaiSubsite that ignores the parents middleware. Maybe there is a better name then WaiSubsiteWithAuth? From what I understand this will also pick up whatever middleware the parent site has.

[snoyberg]

This looks good. Could you additionally:

• Bump the minor version number
• Make an entry in the ChangeLog
• Add a Haddock comment to WaiSubsite explaining the difference from WaiSubsiteWithAuth
• Add a Haddock comment to WaiSubsiteWithAuth referring to WaiSubsite's docs, and a @since annotation for the new version

[mchaver]

Looks like it failed to build in Travis for GHC 8.0.1. Yesod-core built fine but yesod-persistent did not.

[snoyberg]

Thanks! We can ignore the build failure, it's spurious and unrelated.