First pass at v3 layout

`-- latest
    |-- architecture
    |   |-- http_remote_command_execution.html
    |   |-- image_registry.html
    |   |-- kubernetes_model.html
    |   |-- networking.html
    |   |-- openshift_model.html
    |   |-- routing.html
    |   |-- scm.html
    |   `-- ssh_remote_command_execution.html
    |-- image_writers_guide
    |   |-- guidelines.html
    |   `-- sti.html
    |-- installation
    |   |-- docker.html
    |   `-- rpm.html
    |-- v2_changes
    |   |-- applications.html
    |   |-- carts_vs_images.html
    |   `-- terminology.html
    `-- welcome
        |-- doc_guidelines.html
        `-- index.html

Anything v2 specific has been moved under old/ for now.  If this is ok I can start throwing content in there.