Fix typos in require('lib/airport') and regexp for signal_level

Hello Maurice,

This patch fixed two typos in wifiscanner.js and lib/iwlist.js. Namely,

* In wifiscanner.js, changed `require('/lib/airport')` to `require('./airport')` and  `require('/lib/iwlist')` to `require('./iwlist')` to make it work properly.
* In iwlist.js, fixed `'signal_level' : /Signal level(?:=|\:)([-\w]+)/` so that it works with negative signal levels.
* Restructured the codebase so that it looks neater. wifiscanner.js is moved to lib/, and scanner.js and geolocation.js are moved into examples/ . package.json is updated to reflect this change.

Also I can't find this project on npm, would be great if you can publish it. That's all. Thanks.

Regards,
xkxx.