Give ability to change the default get separator

[gallofeliz]

Hi,

As it is possible to use "_" for env() and argv() (or '-'), it should be good te be able to configure the get separator.

Example :

{
    "database": {
        "user": "root"
    }
}

I would like to get database:user doing nconf.get('database.user'). It's more natural.

Regards