Generate settings pages automatically.

This adds metadata to settings fields that can be used to automatically
generate the settings window. For now I have replaced the Difficulty
page. Will follow up to replace the others.

game/settings/boundedfloatoption.py

@@ -0,0 +1,31 @@
+from dataclasses import dataclass, field
+from typing import Any, Optional
+
+from .optiondescription import OptionDescription, SETTING_DESCRIPTION_KEY
+
+
+@dataclass(frozen=True)
+class BoundedFloatOption(OptionDescription):
+    min: float
+    max: float
+    divisor: int
+
+
+def bounded_float_option(
+    text: str,
+    page: str,
+    section: str,
+    min: float,
+    max: float,
+    divisor: int,
+    detail: Optional[str] = None,
+    **kwargs: Any,
+) -> float:
+    return field(
+        metadata={
+            SETTING_DESCRIPTION_KEY: BoundedFloatOption(
+                page, section, text, detail, min, max, divisor
+            )
+        },
+        **kwargs,
+    )