Update changelog

changelog.d/1556

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+synopsis: Display capture hints in router layout
+prs: #1556
+
+description: {
+
+This PR introduces a CaptureHint type, which is passed as an extra argument to the CaptureRouter and CaptureAllRouter constructors for the Router' type.
+CaptureHint values are then used in routerLayout, to display the name and type of captured values, instead of just <capture> previously.
+
+N.B.:
+Because the choice smart constructor for routers can aggregate Capture combinators with different capture hints, the Capture*Router constructors actually take a list of CaptureHint, instead of a single one.
+
+This PR also introduces Spec tests for the routerLayout function.
+
+Warning:
+This change is potentially breaking, because it adds the constraint `Typeable a` to all types that are to be captured. Because all types are typeable since GHC 7.10, this is not as bad as it sounds ; it only break expressions where `a` is quantified in an expression with `Capture a`.
+In those cases, the fix is easy: it suffices to add `Typeable a` to the left-hand side of the quantification constraint.
+
+}