Add codesnippet for almost chronological order

Such as for downloading hashtag feeds, as discussed in #666 and contributed by
@e2tovar.

Also change comment color to grey in codesnippets in documentation.

docs/codesnippets/121_since_until.py

@@ -5,13 +5,11 @@ import instaloader
 
 L = instaloader.Instaloader()
 
-posts = instaloader.Hashtag.from_name(L.context, 'urbanphotography').get_posts()
-# or
-# posts = instaloader.Profile.from_username(L.context, PROFILE).get_posts()
+posts = instaloader.Profile.from_username(L.context, "instagram").get_posts()
 
 SINCE = datetime(2015, 5, 1)
 UNTIL = datetime(2015, 3, 1)
 
 for post in takewhile(lambda p: p.date > UNTIL, dropwhile(lambda p: p.date > SINCE, posts)):
     print(post.date)
-    L.download_post(post, '#urbanphotography')
+    L.download_post(post, "instagram")

docs/codesnippets/666_historical_hashtag_data.py

@@ -0,0 +1,30 @@
+from datetime import datetime
+import instaloader
+
+L = instaloader.Instaloader()
+
+posts = instaloader.Hashtag.from_name(L.context, "urbanphotography").get_posts()
+
+SINCE = datetime(2020, 5, 10)  # further from today, inclusive
+UNTIL = datetime(2020, 5, 11)  # closer to today, not inclusive
+
+k = 0  # initiate k
+k_list = []  # uncomment this to tune k
+
+for post in posts:
+    postdate = post.date
+
+    if postdate > UNTIL:
+        continue
+    elif postdate <= SINCE:
+        k += 1
+        if k == 50:
+            break
+        else:
+            continue
+    else:
+        L.download_post(post, "#urbanphotography")
+        k = 0  # set k to 0
+        # if you want to tune k, uncomment below to get your k max
+        #k_list.append(k)
+#max(k_list)