Browsing to http://www.logstash.net/docs/1.1.10/extending/example-add-a-new-filter or pretty much and input/output has a big red box at the top advising people where to find the 1.5.0 docs. However those links all point to dead pages.
Sorry you're having a hard time with that. We'll work to correct the links, but we'll be eliminating the old logstash.net shortly. Please look to http://elastic.co/guide/en/logstash/current/index.html for all current documentation.
We've noted a few of these in this ticket https://github.com/elastic/logstash/issues/3359 and will resolve it soon. Sorry for the bumps in the road while we clean up some of the lost links during our migration to elastic.co! <3