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XML extractor support #1

* implemented simple http connector
* xml extractor
XML extractor support #1

* creating InputSource for XmlExtractor on the fly instead of using the same InputSource which causes an exception (obviously) on another attempt to get xml data
* renamed http connector interface
Source filtering on transform #4

* transform filter which gives additional mechanism to do a pre process of source data
Merge branch 'master' of github.com:aveprev/link-etl