Add basic functions and tests, set default language, strict, verbose.

This takes the old "get_single_trans" and "get_lang_trans" from
ReadTranslations.pm, but I've added more robustness and
consistency. If the "strict" option is off, it just tries to find
anything valid-looking to return. If the "strict" option is on, it
dies whenever it reaches a point where a translation seems to be
missing (undefined, rather than blank).

I've also added a "verbose" option for printing debugging messages,
and two test files, as well as basic retrieval testing, and setting of
default language.