Implement Guild.fetch_members

Also implements `MemberIterator`.

discord/iterators.py

@@ -587,3 +587,44 @@ class GuildIterator(_AsyncIterator):
                 self.limit -= retrieve
             self.after = Object(id=int(data[0]['id']))
         return data
+
+class MemberIterator(_AsyncIterator):
+    def __init__(self, guild, limit=1, after=None):
+
+        if isinstance(after, datetime.datetime):
+            after = Object(id=time_snowflake(after, high=True))
+
+        self.guild = guild
+        self.limit = limit
+        self.after = after or OLDEST_OBJECT
+
+        self.state = self.guild._state
+        self.get_members = self.state.http.get_members
+        self.members = asyncio.Queue(loop=self.state.loop)
+
+    async def next(self):
+        if self.members.empty():
+            await self.fill_members()
+
+        try:
+            return self.members.get_nowait()
+        except asyncio.QueueEmpty:
+            raise NoMoreItems()
+
+    async def fill_members(self):
+        if self.limit > 0:
+            retrieve = self.limit if self.limit <= 1000 else 1000
+
+            after = self.after.id if self.after else None
+            data = await self.get_members(self.guild.id, retrieve, after)
+
+            if data:
+                self.limit -= retrieve
+                self.after = Object(id=int(data[-1]['user']['id']))
+
+            for element in reversed(data):
+                await self.members.put(self.create_member(element))
+
+    def create_member(self, data):
+        from .member import Member
+        return Member(data=data, guild=self.guild, state=self.state)