Code generation of preconditioning functions

[Arun-R-M]

Note: code modification to use local packages not to be adopted in master

Main Changes

• In Python, generate a C file (via CasADi) with the preconditioning parameters (the w's and ρ).

Associated Issues

• Addresses #107

TODOs

• [x] Documentation
• [x] All tests must pass
• [x] Update CHANGELOG(s)
• [x] ~Update webpage documentation~
• [x] Bump versions (in CHANGELOG, Cargo.toml and VERSION)