Add new CUTEst routines for the John function

[jfowkes]

Resolves #68

Add interfaces for some new CUTEst routines for the (Fritz) John function, defined as

$$ \mathcal{J}(x,\lambda_0,\lambda) = \lambda_0 f(x) + \langle \lambda, c(x) \rangle $$

For more details please see https://en.wikipedia.org/wiki/Fritz_John_conditions

• [x] cdhj: evaluate the dense Hessian of the (Fritz) John function
• [x] cshj: evaluate the sparse Hessian of the (Fritz) John function
• [x] chjprod: product of Hessian of the (Fritz) John function with a vector
• [x] cohprods: sparse product of (objective) Hessian with a vector
• [ ] Determine CUTEst version and use this to decide which routines to expose
• [ ] Add suitable sections to Problem Methods section of docs for clarity

For the full list of newly added CUTEst functions please see #68

[jfowkes]

@jess-farmer this is now ready for you, please test and let us know if it all works:

1. Please compile the latest version of CUTEst (see our PyCUTEst README)
2. Checkout and install this branch of PyCUTEst: pip install -e .

For full details of PyCUTEst usage please see our extensive documentation.