function getUserExtensionPath() {
        if (brackets.app.getApplicationSupportDirectory) {
            return brackets.app.getApplicationSupportDirectory() + "/extensions/user";
        }

        return null;
    }
Returns the full path of the default user extensions directory. This is in the users
application support directory, which is typically
/Users/<user>/Application Support/Brackets/extensions/user on the mac, and
C:\Users\<user>\AppData\Roaming\Brackets\extensions\user on windows.