Add discord.utils.sleep_until helper function

discord/utils.py

@@ -338,6 +338,24 @@ async def sane_wait_for(futures, *, timeout):
 
     return done
 
+async def sleep_until(when):
+    """Sleep until a specified time.
+
+    If the time supplied is in the past this function will yield instantly.
+    
+    Parameters
+    -----------
+    when: :class:`datetime.datetime`
+        The timestamp in which to sleep until.
+
+    .. versionadded:: 1.3.0
+    """
+    if when.tzinfo is None:
+        when = when.replace(tzinfo=datetime.timezone.utc)
+    now = datetime.datetime.now(datetime.timezone.utc)
+    delta = (when - now).total_seconds()
+    await asyncio.sleep(max(delta, 0))
+
 def valid_icon_size(size):
     """Icons must be power of 2 within [16, 4096]."""
     return not size & (size - 1) and size in range(16, 4097)