base: Add changelog entry for withTypeable generalization
base: Add changelog entry for withTypeable generalization

sdiehl/ghc,sdiehl/ghc,shlevy/ghc,ezyang/ghc,ezyang/ghc,ezyang/ghc,ezyang/ghc,sdiehl/ghc,shlevy/ghc,ezyang/ghc,shlevy/ghc,shlevy/ghc,shlevy/ghc,ezyang/ghc,sdiehl/ghc,sdiehl/ghc,sdiehl/ghc,shlevy/ghc,sdiehl/ghc,ezyang/ghc,shlevy/ghc