fix to add an custom callback if wrong url

if the url do not link to RSS Feed, responseData is null and throws
an error while reading the property feed
the option callbackWrongURL makes the use of custom error handling
possible
rename callbackWrongURL
Replaced forEach with jQuery's $.each to support browsers without native support of forEach
Merge pull request #15 from aegisrunestone/gh-pages

"Fixed" forEach
Merge branch 'patch-1' of git://github.com/eliten00b/jquery-rss into eliten00b-patch-1
fixed broken error callback + added success callback
changed in 1.3.0
v1.3.0