I just put together a few C and Julia files that let users read models in the AMPL modeling language for optimization.
https://github.com/dpo/ampl.jl It's not quite a module or a package; please bear with me as I'm still learning Julia. This gives access to a huge collection of problems already written in AMPL, e.g., http://orfe.princeton.edu/~rvdb/ampl/nlmodels/index.html https://github.com/mpf/Optimization-Test-Problems (many of the same problems, without the solve command) http://netlib.org/ampl/models/ etc. AMPL computes first and second derivatives for you, so it should be easy to pass such problems to solvers written in Julia, and to write solvers around this model format. Cheers.
