Support ManualNLPModel #22
Description
Must add ManualNLPModel in
https://github.com/paraynaud/PartiallySeparableNLPModels.jl/blob/23eaa69b9b7779492b89ed77369bd9f07e6cdb31/src/partitioned_data/partitionedNLPModels/partitionedNLPModel.jl#L15
Define a new get_expr_tree(::ManualNLPModel) similar to
https://github.com/paraynaud/PartiallySeparableNLPModels.jl/blob/23eaa69b9b7779492b89ed77369bd9f07e6cdb31/src/partitioned_data/partitionedNLPModels/partitionedNLPModel.jl#L23
The rest of the code should be fine.