Add syntatic sugar for route registration

This takes a popular API whereby instead of passing the HTTP method as
an argument to route it is instead used as the method name i.e.

    @app.route("/", methods=["POST"])

is now writeable as,

    @app.post("/")

This is simply syntatic sugar, it doesn't do anything else, but makes
it slightly easier for users.

I've included all the methods that are relevant and aren't auto
generated i.e. not connect, head, options, and trace.

tests/test_basic.py

@@ -48,6 +48,23 @@ def test_options_on_multiple_rules(app, client):
     assert sorted(rv.allow) == ["GET", "HEAD", "OPTIONS", "POST", "PUT"]
 
 
+@pytest.mark.parametrize("method", ["get", "post", "put", "delete", "patch"])
+def test_method_route(app, client, method):
+    method_route = getattr(app, method)
+    client_method = getattr(client, method)
+
+    @method_route("/")
+    def hello():
+        return "Hello"
+
+    assert client_method("/").data == b"Hello"
+
+
+def test_method_route_no_methods(app):
+    with pytest.raises(TypeError):
+        app.get("/", methods=["GET", "POST"])
+
+
 def test_provide_automatic_options_attr():
     app = flask.Flask(__name__)