Create ad_placeholders.txt

Sublist for filters related to empty advertising placeholders.

The intention with this sublist is to remove all of these currently existing filters from `utlralist.txt` so eventually `ultralist.txt` is ONLY a list that exists to subscribes to all sublists. This will allow the flexibility for users to only subscribe to certain features of ultralist.txt e.g. only remove newsletter & empty ad boxes but don't change any CSS elements like sticky headers. (e.g. don't subscribe to `css_style_filters.txt`

Relates to #67

filters/ad_placeholders.txt

@@ -0,0 +1,13 @@
+! Title: Web Annoyances Ultralist - Ad Placeholder Filters
+! Last Modified: 12:34 2019-12-06
+! Expires: 2 Days (Update Frequency)
+! Description: Web Annoyances Ultralist Sublist for empty advertising placeholders.
+! Homepage: https://github.com/yourduskquibbles/webannoyances
+! Discord: https://discord.me/yourduskquibbles
+! Issues: https://github.com/yourduskquibbles/webannoyances/issues
+! License: https://creativecommons.org/licenses/by-sa/4.0
+! Copyright: © 2016-2019 by yourduskquibbles
+! Works best with uBlock Origin or Nano Adblocker - be sure to install it as well!
+
+! Start Web Annoyances Ultralist - Ad Placeholder Filters
+nbcsports.com###topbanner