Merge pull request #5 from craigcarnell/fix/elasticsearch.xml

fix template for graylog2-elasticsearch.xml
fix typo in dependencies.pp
Merge pull request #6 from kgeis/patch-1

fix typo in dependencies.pp
Changes docs to be consistent with the codebase.
Merge pull request #7 from typhonius/patch-1

Changes docs to be consistent with the codebase.
Release v2.0.15
Merge branch 'master' into fix/0.20.0-download-link