Augmented Lagrangian Method: Python code generator

[alphaville]

Work in progress - do not merge yet

TODOs:

• Update API
  • [x] link to latest rust library (v0.6.1-alpha.1)
  • [x] update opengen.builder.problem with new data (mappings, etc)
  • [x] constraints in Python: implement distance functions
  • [x] Euclidean Ball
  • [x] Infinity Ball
  • [x] Rectangle
  • [x] Second-order cone (see #93 and https://github.com/casadi/casadi/issues/2491)
  • [x] Cartesian product of the above
• C code generation
  • [x] define new cost function psi in builder (see #99)
  • [x] update C interface, interface.c (see #99)
  • [x] build code for mappings F1 and F2 using CasADi
• Rust-to-C interface
  • [x] extend Rust-to-C interface to auto-generated functions in extern
  • [x] Question: do we need a C header file in extern? Do we need extern/Makefile?
• Rust code generation
  • [x] Update basic template
  • [x] Update TCP/IP server template
• [x] Update CHANGELOG