MAHOUT-1463: Modify OnlineSummarizers to use the TDigest dependency from Maven Central

git-svn-id: https://svn.apache.org/repos/asf/mahout/trunk@1578179 13f79535-47bb-0310-9956-ffa450edef68
Fixing some URLs and cleaning up language

git-svn-id: https://svn.apache.org/repos/asf/mahout/trunk@1578215 13f79535-47bb-0310-9956-ffa450edef68