Refactor app in to its own slice

slices/main/actions/key/show.rb

@@ -0,0 +1,13 @@
+module Main
+  module Actions
+    module Key
+      class Show < Action
+        include Deps["settings"]
+        def handle(req, res)
+          res.content_type = "text/plain"
+          res.body = settings.micropub_pub_key
+        end
+      end
+    end
+  end
+end