exc_bad_access when dismissing MWFeedParser delegate

[alarrosa14]

I had exc_bad_access when dismissed the MWFeedParser delegate view controller before all parsing labours were done.

I could fix this by making the delegate definition weak:

// MWFeedParser.h
@property (nonatomic, weak) id <MWFeedParserDelegate> delegate;

I also had to delete the private redefinition:

id <MWFeedParserDelegate> __unsafe_unretained delegate;