Refactored output parameters of update.

[lewie-donckers]

Refactored the output parameters of Controller::update() and Controller::update_with_limits() to return values.

See:

• https://isocpp.github.io/CppCoreGuidelines/CppCoreGuidelines#f20-for-out-output-values-prefer-return-values-to-output-parameters
• https://isocpp.github.io/CppCoreGuidelines/CppCoreGuidelines#f21-to-return-multiple-out-values-prefer-returning-a-struct-or-tuple