Use diagnostics inside JuMP [work in progress]

[fonsp]

See #18

Right now I just changed the field types for control values to Real instead of Float64, to allow JuMP to call our diagnostic functions with its Dual number type.

Changing the field types of a struct from concrete (like Float64 or Vector{Float64}) to abstract (like Real or Vector{<:Real}) can impact performance, so I will have to look into this first :)