Code: Missing mdwps

[Andy Nowacki]

This function is referred to in the docs, but does not exist in the code. Either update the code to add it or remove it from the docs.

[Charlotte Haley]

Updated the docs in this commit with the proper function signature, and added entries for the multivariate version, the mdslepian function, and the gpss function.

[Andy Nowacki]

Thanks—this can be closed now.