HDFS side of HADOOP-8427. The src/main/docs/src/documentation/content/xdocs contents needs to be converted to APT and removed.
Split MapReduce and YARN sections in documentation navigation
Move Federation and WebHDFS documentation into HDFS project
Convert Forrest docs to APT, incremental
Closing as fixed, since this was done eons ago.
Note we need to also move some HDFS docs from MR to HDFS.