docs: fix mistakes in code examples for routing

Fixes #616

solara/website/pages/documentation/advanced/content/20-understanding/40-routing.md

@@ -68,7 +68,7 @@ If you do define a `Page` component, you are fully responsible for how routing i
 An example route definition could be something like this:
 
 ```python
-import solara as sol
+import solara
 
 routes = [
     # route level == 0
@@ -103,7 +103,7 @@ routes = [
 @solara.component
 def Page():
     level = solara.use_route_level()  # returns 0
-    route_current, routes_current_level = solara.use_routes()
+    route_current, routes_current_level = solara.use_route()
     # route_current is routes[1], i.e. solara.Route(path="docs", children=[...])
     # routes_current_level is [routes[0], routes[1], routes[2], routes[3]], i.e.:
     #    [solara.Route(path="/"), solara.Route(path="docs", children=[...]),
@@ -125,7 +125,7 @@ Now the `MyFirstLevelChildComponent` component is responsible for rendering the
 @solara.component
 def MyFirstLevelChildComponent():
     level = solara.use_route_level()  # returns 1
-    route_current, routes_current_level = solara.use_routes()
+    route_current, routes_current_level = solara.use_route()
     # route_current is routes[1].children[0], i.e. solara.Route(path="basics", children=[...])
     # routes_current_level is [routes[1].children[0], routes[1].children[1]], i.e.:
     #    [solara.Route(path="basics", children=[...]), solara.Route(path="advanced")]
@@ -143,7 +143,7 @@ And the `MySecondLevelChildComponent` component is responsible for rendering the
 @solara.component
 def MySecondLevelChildComponent():
     level = solara.use_route_level()  # returns 2
-    route_current, routes_current_level = solara.use_routes()
+    route_current, routes_current_level = solara.use_route()
     # route_current is routes[1].children[0].children[0], i.e. solara.Route(path="react")
     # routes_current_level is [routes[1].children[0].children[0], routes[1].children[0].children[1], routes[1].children[0].children[2]], i.e.
     #    [solara.Route(path="react"), solara.Route(path="ipywidgets"), solara.Route(path="solara")]