Refactor micropub specific things out to a slice

config/providers/param_parser.rb

@@ -2,7 +2,7 @@
 
 Hanami.app.register_provider :param_parser, namespace: true do
   start do
-    register "micropub_post", Adamantium::MicropubRequestParser.new
+    register "micropub_post", Micropub::RequestParser.new
     register "webmention", Adamantium::WebmentionRequestParser.new
   end
 end