Add library for pattern matching

Add new library that build regular expressions for pattern matching.
Extract year in date matcher
Mark error TODO
Merge branch 'master' of github.com:gbirke/scrapy-vivo
Add MultiExport extension

MultiExport is a subclass of FeedExporter extension. At the moemnt,
close_spider is not working right - something about maybeDeferred?
Bugfix for deferred feed export

Callback that ware already called are no longer added to deferred.