Fixed support for the supportedLngs option

options.supportedLngs was being overwritten in i18n.init();

Extended the behaviour of options.supportedLngs, now allowing:
- RegExp or any object implementing a '.test(locale)' method;
- array-like object listing valid locales;
- string for a single locale option;
- false for disabling locale validation (accepting any value);

Defaults to a RegExp, matching any "locale-like" value, such as: 'en',
'en-US', 'en_UK', 'zh-Hans-HK', 'ast', etc;

The supportedLngs option now affects the querystring method for setting
locales too;