Manifest sections support

Resolves #1698 by adding support for manifest sections: "lein test" runs ok and I updated the sample project as well.

Both the following test cases produce correct manifests:

    [
       ["K" "J"]
       [:my-section-1 {"C" "D" "S" "T"}]
       ["A" "B"]
       [:my-section-2 [["E" "F"] ["X" "Y"]] ]
       ["G" "H"]
    ]

    {
       "K" "J"
       :my-section-1 {"C" "D" "S" "T"}
       "A" "B"
       :my-section-2 [["E" "F"] ["X" "Y"]]
       "G" "H"
    }