Improve several stubs. (math, _random, time, etc.)

Some of these are derived from mypy/stubs/.

2.7/_random.pyi

@@ -1,20 +1,12 @@
-"""Stub file for the '_random' module."""
-# This is an autogenerated file. It serves as a starting point
-# for a more precise manual annotation of this module.
-# Feel free to edit the source below, but remove this header when you do.
+# Stubs for _random
 
-from typing import Any, List, Tuple, Dict, GenericType
+from typing import Optional, Any
 
 class Random(object):
-    def getrandbits(a: int) -> Any:
-        raise MemoryError()
-        raise ValueError()
-    def getstate() -> tuple: ...
-    def jumpahead(*args, **kwargs) -> None:
-        raise TypeError()
-    def random() -> float: ...
-    def seed(*args, **kwargs) -> None:
-        raise MemoryError()
-    def setstate(*args, **kwargs) -> None:
-        raise TypeError()
-        raise ValueError()
+    def __init__(self, seed: x: object = None) -> None: ...
+    def seed(self, x: object = None) -> None: ...
+    def getstate(self) -> tuple: ...
+    def setstate(self, state: tuple) -> None: ...
+    def random(self) -> float: ...
+    def getrandbits(self, k: int) -> int: ...
+    def jumpahead(self, i: int) -> None: ...