Improve CAPI

[jbreue16]

Open ends from #115 as documented by @schmoelder :

TODO

• On unit operation level, WRITE_SOLUTION_LAST_UNIT could be renamed to WRITE_SOLUTION_LAST. I don't think anyone is using this feature yet so a breaking change is justifiable in my opinion.
• WRITE_SOLDOT_LAST(_UNIT) is completely missing; at least in the documentation. Check if it works.
• Same for WRITE_SENS_LAST(_UNIT) and WRITE_SENSDOT_LAST(_UNIT).
• (Maybe) Rename LAST_STATE_SENSY_XXX => LAST_STATE_SENS_XXX, and LAST_STATE_SENSYDOT_XXX => LAST_STATE_SENSDOT_XXX (breaking change in output might break some stuff)
• Currently, the order of dimensional arguments in the API is different from the order of the dimensions in the state vector. If possible, we should fix this to make it more consistent. I can foresee stupid implementation errors in the future... 🙈