Handling errors via py bindings

[alphaville]

Main Changes

The main change is that now when using the Python bindings, aka direct interface, the API mirrors the API of the TPC interface. In other words,

import rosenbrock

solver = rosenbrock.solver()
response = solver.run(p=[0.5, 8.5], initial_guess=[1, 2, 3, 4, 0])

and response is an instance of SolverResponse and should be handled as follows:

if response.is_ok():
    # SolverResponse
    result = response.get()
    print(result)
else:
    # SolverError
    error = response.get()
    print(type(error))

Associated Issues

• Closes Better error handling via Python bindings #409

Merge Dependencies

This will be merged into dev/release. It should rather be merged before #404.

Target versions

• OpEn version 0.12.0
• opengen version 0.11.0 (including breaking changes!)

Checklist

• API documentation updated
• Appropriate testing
• Update CHANGELOG(s)
• Update webpage documentation, if necessary
• Bump versions (in CHANGELOG, Cargo.toml and VERSION), if necessary