feat: Return result for all possible combintations of columns

[roshnet]

Feature Request 🎉

Description

To find the score, two columns (namely the params x and y in ppscore.score()) need to be supplied in call to score().
It would be nice to have a functionality where the user can get an array of results corresponding to all columns in a single line of code.

For instance, if comparisons between columns 'A', 'B', 'C', and 'D' are to be made, it should be possible to do so with a single line of code. Results could be obtained as a list of comparisons between A-B, A-C, A-D, B-C, B-D, and C-D.

Possible Solution

This can be achieved in two ways -

1. create another function which iterates over all possible combinations and yields/returns a list
2. add logic to existing implementation of score for the same.

Regarding test cases, it'd be easier to write a new one for a new function (as per 1), rather than modifying the existing implementation.

Remarks

@8080labs I'd like to work on it.

[mankoff]

@roshnet how is this different than the pps.matrix function shown in https://github.com/8080labs/ppscore/blob/master/README.md?
https://github.com/8080labs/ppscore/blob/master/src/ppscore/calculation.py#L297

[roshnet]

Ah, I was unaware of it at the moment. Thanks @mankoff for pointing out.
I guess this issue can be closed now.