MOD: wind retrieval check

Slight modification of the _check_analysis function, mainly for easier
readability of the output dictionary.
MOD: minor changes

Minor changes to the _check_analysis function in winds.py
MOD: significant changes coming

First I am going back to explicitly writing every parameter in the call
to solve_wind_field() instead of using **kwargs. I believe this is the
more Pythonic way of doing things. Second, I am beginning to add the
impermeability condition as a strong constraint rather than a weak
constraint. Actually I plan to have both options available. Future
changes will likely include a better way to implement the cost function
and its Jacobian (gradient) and remove altogether cga.py