Change variable names in the gaussian fittings

[ShinjiFujita]

Changed variable names in the gaussian fitting results.
Params are stored in dict (fit_res_params_dict).

[astropenguin]

My apologies for the long silence to check your updates. It looks no problem, but let me update the following points in terms of the package being used as a command line tool:

1. Let us use Python's logging for the notification on a 2D Gaussian fit failure. As a command line tool (decode-qlook), outputting such information to stdout is sometimes not wanted, for example, when another tool is connected to by a pipe to use the return value of decode-qlook (i.e. path of the final product). Using Python's logging allows users to fully control the notification style, so I think it would merit more.
2. Let me add missing return type hints and docstrings of the function you added. If you feel that they are not appropriate, please feel free to let me know or raise another issue/PR.

[astropenguin]

This closed #218.