RSS 'initialAnnounceHeadlines' variable changed to Integer.

Zero can be used for 'initialAnnounceHeadlines' in RSS plugin.
Merge branch 'testing' of github.com:slackhead/Limnoria into testing
Merge pull request #583 from slackhead/testing

RSS: Edit 'initialAnnounceHeadlines' from PositiveInteger to Integer to allow use of 0 (zero).