Added a configuration file, and some refactoring.

That's a lot of changes in one go, but I put them in different commits.

I added a configuration file in “~/.livla/config.json”. Since some code had to be repeated, I created some functions to do the job. 

I also moved the `var fs = require("fs"), path = require("extra-path")` to the top of the script, having checked that they are never redefined to something else than these modules.

Oh, and I put a link to the lojban wiki page that talks about this bot in the README.md. I realize that the link was in the code (as a real name for the bots), but I hope this will give it a little more visibility (eh, I missed it ;-P).