Order fields and errors response improvements

We have improved order fields to ease the integration and understanding of the amounts.

Amount fields

Some fields were added in the order's generation and querying endpoint response:

Before we had:

{
    "value_to_receive": "50.00",
    "fee_value": "0.55",
    ... other fields
}

Now we have:

{
    "value": 50.0, # orders initial amount
    "paid_value": 50.0, # amount paid by user
    "fee_value": 1.0, # orders fee
    "liquid_value": 49.0, # amount available in merchant account
    ... other fields
}

Errors response

We have improved the way that errors are returned.

Before we had:

{
    "errors": {
        "currency": "Required field.",
        "payer": {
            "documentType": "Required field.",
            "documentNumber": "Required field."
        }
    }
}

Now we have:

{
    "errors": {
        "currency": "Required field.",
        "documentType": "Required field.",
        "documentNumber": "Required field."
    }
}