Fixup haddock markup in PersistStore
Fixup haddock markup in PersistStore

'@since' must be a paragraph on its own, otherwise it remains
uninterpreted. Verified locally via `cabal haddock`.

psibi/persistent,bitemyapp/persistent,gbwey/persistent,yesodweb/persistent,creichert/persistent,plow-technologies/persistent,gbwey/persistent,paul-rouse/persistent,erikd/persistent,gbwey/persistent,naushadh/persistent