Add preliminary Latin (LA) support

[sgharms]

Known issues surround ambiguity based on the subjective case. Latin uses the subjective AND genitive cases to know which form a noun takes. ActiveSupport::Inflector assumes this is knowable solely based on the subjective case. Consequently in cases of ambiguity, where the genitive case would decide the issue, we come up with these problems:

First

/us$/ (2nd decl, masc) versus /us$/ (4th decl, genderd)

Second

Third declension nouns -- all of them where we can't know from the subjective case what base to use. How to handle that both 'arx' and 'corpus' should fall here?

Nevertheless, we do make a step forward in this commit.

[davidcelis]

If these cover the typical and majority of cases, then I'm happy. I'm not terribly interested in trying to catch every case; that's where Rails core went wrong ;)

[sgharms]

I've opened a discussion in ActiveSupport just to try to see if a possible solution I can envision has any legs: https://github.com/rails/rails/issues/13205