Added ethnologue command

Completing [this GCI 2013 task](https://google-melange.appspot.com/gci/task/view/google/gci2013/4554769062428672).
Syntax: `.ethnologue <lg>` where "lg" can be an ISO-639-3 code or language name. If only one language name matches, it assumes that one; else, it gives a list of possible ISO-639-3 codes.
Also fixed `.seen` bug