By default, CsvEncoder decoding process explodes the headers automatically based on the . character to generate nested arrays, the separation character being configurable based on our needs. For instance:

username,birth.day,birth.month,birth.year
deuchnord,9,6,1993

Would result in the following PHP array:

[
    "username" => "deuchnord",
    "birth" => [
        "day" => 9,
        "month => 6,
        "year" => 1993
    ]
]

This is a very nice feature, but in some cases, we prefer to skip the generation of those nested arrays.
This PR provides a way to disable it by simply setting the already existent CsvEncoder::KEY_SEPARATOR_KEY option to false, so the same CSV above now results to:

[
    "username" => "deuchnord",
    "birth.day" => 9,
    "birth.month => 6,
    "birth.year" => 1993
]