move download files to site-docs

git-svn-id: https://svn.apache.org/repos/asf/maven/shared/trunk@1632931 13f79535-47bb-0310-9956-ffa450edef68
prepare version 21 release

git-svn-id: https://svn.apache.org/repos/asf/maven/shared/trunk@1632932 13f79535-47bb-0310-9956-ffa450edef68
[maven-release-plugin] prepare release maven-shared-components-21

git-svn-id: https://svn.apache.org/repos/asf/maven/shared/trunk@1632933 13f79535-47bb-0310-9956-ffa450edef68
[maven-release-plugin] prepare for next development iteration

git-svn-id: https://svn.apache.org/repos/asf/maven/shared/trunk@1632935 13f79535-47bb-0310-9956-ffa450edef68