Add vectorised signatures for categorical, categorical_logit, and ordered_logistic

[andrjohns]

This Math PR vectorises the RNGs and lpmfs of the ordered_logistic, categorical, and categorical_logit distrubtions.

The following signatures were added:

• ordered_logistic_rng(vector, vector)
• ordered_logistic_rng(vector, vector[])
• ordered_logistic_rng(real, vector[])
• categorical_lpmf(int, vector[])
• categorical_lpmf(int[], vector[])
• categorical_rng(vector[])
• categorical_logit_lpmf(int, vector[])
• categorical_logit_lpmf(int[], vector[])
• categorical_logit_rng(vector[])

I'll add these signatures once the PR goes through

[WardBrian]

The linked math PR never got merged -- still planning on it?