Repository Metadata
Plugins need maven-metadata.xml files listing all plugins available in a groupId
for instance http://repo1.maven.org/maven2/org/apache/maven/plugins/maven-metadata.xml
All artifacts need maven-metadata.xml listing all versions, although only for some operations, like version ranges
eg http://repo1.maven.org/maven2/org/apache/maven/maven-artifact/maven-metadata.xml
Snapshot artifacts need maven-metadata.xml in the version folder to resolve snapshots
