Dfo-ls

---------------------------
* Handle finitely many arbitrary convex constraints in addition to simple bound constraints.
* Add module-level logging for more informative log outputs.
* Only new functionality is added, so there is no change to the solver for unconstrained/bound-constrained problems.

---------------------------
* Minor update to customise handling of NaNs in objective evaluations - no changes to the DFO-LS algorithm.

---------------------------
* Minor update to remove NumPy deprecation warnings - no changes to the DFO-LS algorithm.

---------------------------
* Make the use of the `trustregion <https://github.com/lindonroberts/trust-region>`_ package optional, not installed by default.

-------------------------
* Use deterministic initialisation by default (so it is no longer necessary to set a random seed for reproducibility of DFO-LS results).
* Full model Hessian stored rather than just upper triangular part - this improves the runtime of Hessian-based operations.
* Faster trust-region and geometry subproblem solutions in Fortran using the `trustregion <https://github.com/lindonroberts/trust-region>`_ package.
* Faster interpolation solution for multiple right-hand sides.
* Don't adjust starting point if it is close to the bounds (as long as it is feasible).
* Option to stop default logging behavior and/or enable per-iteration printing.
* Bugfix: correctly handle 1-sided bounds as inputs, avoid divide-by-zero warnings when auto-detecting restarts.

--------------------------
* Link code to Zenodo, to create DOI - no changes to the DFO-LS algorithm.