Improve handling of generics

[wleoncio]

The internal generic functions in R/generics.R are used by the following exported functions:

• [x] Koopman_asymptotic_score_CI_2x2
• [x] Mee_asymptotic_score_CI_2x2
• [x] MiettinenNurminen_asymptotic_score_CI_difference_2x2
• [x] MiettinenNurminen_asymptotic_score_CI_OR_2x2
• [x] MiettinenNurminen_asymptotic_score_CI_ratio_2x2
• [x] Uncorrected_asymptotic_score_CI_2x2

So far, methods are being called directly, but that is not ideal. Ideally, they should only call the generics and have the generics handle the dispatching.

[wleoncio]

414c6ce fixed this satisfactorily. Methods still need to be explicitly called when used as an argument of uniroot(), though, but at least the methods only need a simple renaming to work now.