Move the built in plugins to their own repos. For example, mapper-attachments moved to https://github.com/elasticsearch/elasticsearch-mapper-attachments. This also means new installation path, for mapper-attachments, the installation is: bin/plugin -install elasticsearch/elasticsearch-mapper-attachments/1.0.0.

All plugins will start with version 1.0.0, and have compatibility matrix between the plugin version and the elasticsearch version supported. All plugins will work with 0.18.5 and are recommended to be installed from their new repos compared to using the shorthand notion.

This move will help both with more samples to how to build external plugins, and simplify the elasticsearch project. Note, all the plugins are using maven as the build file to simplify people using it.