Testing file conversion

Was having some issues with my editor converting fileencoding, making
git flag the whole file as changed.
Converting file before changes

Seems that the files are being converted by git (not my editor) when I
commit. This makes the whole file look to be changed loosing actual
changes made to the file.
Fixed bugs related to opts.supportedLngs

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

Extended opts.supportedLngs, now supporting:
- a RegExp or any object implementing a '.test(locale)' method;
- a array-like object listing valid locales;
- a string defining a single valid locale;
- 'false', disabling all locale validation (accepts any value);

opts.supportedLngs now defaults to a RegExp matching any "locale-like"
string, such as: 'en', 'en-US', 'en_US', 'en-us', 'ast', 'zh-Hans-HK',
etc.;

opts.supportedLngs now affects the querystring method for setting
locales;

Moved the default value assignment for opts.fallbackLng to the same
place as the other default values (in i18next.js). Didn't found any
issues with the change.

With this code, supportedLngs = false should have exactly the same
effect as the former implementation.
opts.supportedLngs is now checked when getting locale from accept-language header

The first locale gotten from accept-language that passes
_isValidLocale() is used as the locale for the request.

_extractLocales() now returns an empty array if there are no headers.
From the former implementation, I understood that it was expected it to
always return an array.