Update analyzed field warning to new docs

[arirubinstein]

The current link is dead: http://www.elastic.co/guide/en/elasticsearch/reference/current/mapping-core-types.html

Updating to the closest-relevant page I could find: http://www.elastic.co/guide/en/elasticsearch/reference/current/mapping.html

[elasticsearch-release]

Jenkins standing by to test this. If you aren't a maintainer, you can ignore this comment. Someone with commit access, please review this and clear it for Jenkins to run; then say 'jenkins, test it'.

[spalger]

Confirmed that @arirubinstein has signed the CLA, though his commits are attributed to his anonymous github email address. That should be fine but getting validation. As for the changes, I think it might make sense to link directly to the field datatypes section, which talked about not_analyzed and multi-fields.

[spalger]

Closed in favor of #5797

[spalger]

Thanks though @arirubinstein!