sa2: propeller_spring -> flying_spring, document flying spring and em level task

.vscode/settings.json

@@ -234,7 +234,7 @@
     "clear_pipe.h": "c",
     "slowing_snow.h": "c",
     "handlers_ia_pipe_horn_sequences.h": "c",
-    "sky_canyon_init.h": "c",
+    "sky_canyon_level_task.h": "c",
     "mon.h": "c",
     "kura_kura.h": "c",
     "star.h": "c",
@@ -325,7 +325,7 @@
     "kubinaga.h": "c",
     "propeller.h": "c",
     "game_3.h": "c",
-    "propeller_spring.h": "c",
+    "flying_spring.h": "c",
     "sprite_data.h": "c",
     "game_2.h": "c",
     "palette_loader.h": "c",