Compatibility for Crystal 0.23.1 and later versions at once

In versions after Crystal 0.23.1, Object#hash was changed to return
an UInt64 instead of a Int32.

This patch always forces hashes to use UInt64.

src/cute.cr

@@ -8,6 +8,10 @@ require "./cute/version"
 # Easy to use event-oriented publisher/subscribe modelled after the
 # Qt Framework.
 module Cute
+  # Type of a connection handle, as returned by the `#on` method of signals and
+  # `#add` of middlewares.
+  alias ConnectionHandle = UInt64
+
   # Creates a *signal*. A signal manages listeners (So called *slots*), which
   # will be called when an event has been *emitted*. Emitting is the act of
   # triggering a signal to announce an event to the listeners.
@@ -246,15 +250,15 @@ module Cute
       end
 
       # Appends a middleware handler
-      def add(&block : Handler)
+      def add(&block : Handler) : ::Cute::ConnectionHandle
         @listeners << block
-        block.hash
+        block.hash.to_u64
       end
 
       # Appends *handler*
-      def add(handler : Handler)
+      def add(handler : Handler) : ::Cute::ConnectionHandle
         @listeners << handler
-        handler.hash
+        handler.hash.to_u64
       end
 
       # Calls the middleware chain.

src/cute/signal.cr

@@ -54,9 +54,9 @@ module Cute
         {{ call.name.stringify }}
       end
 
-      def on(&block : {{ handler_type.id }})
+      def on(&block : {{ handler_type.id }}) : ::Cute::ConnectionHandle
         @listeners << block
-        block.hash
+        block.hash.to_u64
       end
 
       def on(sink : Cute::Sink(U)) forall U
@@ -81,7 +81,7 @@ module Cute
         {% if async %}end{% end %}
       end
 
-      def new_channel : Tuple({{ channel_type.id }}, Int32)
+      def new_channel : Tuple({{ channel_type.id }}, ::Cute::ConnectionHandle)
         ch = {{ channel_type.id }}.new
 
         handle = {% if call.args.empty? %}