Use temporary files during download

This prevents unfinished files from lying around when downloads are
interrupted.
Small fix in RDF serialization example
Merge pull request #86 from Wikidata/partial-dump-downloads

Partial dump downloads
patch some javadoc warnings
Merge pull request #92 from Wikidata/javadoc-fixes

patch some javadoc warnings
Merge branch 'master' into iterable-data

Conflicts:
	RELEASE-NOTES.md