Add preliminary Latin (LA) support

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.