Moved dump file preparation to separate method

This will help to run this in advance later to speed up processing.
Extended logging to provide more information

Especially show some message to let the user know about an ongoing
download.
Processor components for EntityDocuments from revisions

* Revision processor to parse JSON into EntityDocuments
* Interface for classes that process EntityDocuments
Update pom dependencies

* No global default logging configuration for SLF4J
* Use Log4J in examples module
* Make examples depend on other modules
Example program for processing dump files
Inform about directory used for dump files

* Create log message on construction
* Make directory name a public constant for others to use
Print documentation when started
Merge pull request #41 from Wikidata/dump-processing-example

Complete dump processing pipeline + example