Allow converter types on csv import

[jdfergason]

On CSV import allow native series for float64, int64, and string when a Converter is used.

[pjebs]

Can you tell me why you aren't just directly using DictateDataType instead?

[jdfergason]

I am using DictateDataType, but I need custom converters because my CSV file has some null values that are indicated with a '.'.

Here's my code:

DictateDataType: map[string]interface{}{
        DateIdx: imports.Converter{
            ConcreteType: time.Time{},
            ConverterFunc: func(in interface{}) (interface{}, error) {
                return time.Parse("2006-01-02", in.(string))
            },
        },
        symbol: imports.Converter{
            ConcreteType: float64(0),
            ConverterFunc: func(in interface{}) (interface{}, error) {
                v, err := strconv.ParseFloat(in.(string), 64)
                if err != nil {
                    return math.NaN(), nil
                }
                return v, nil
            },
        },
    },

My suggested changes also make the API more consistent. It's confusing to get a SeriesTime as expected but then have the float64 field return SeriesGeneric if using the imports.Converter.

[pjebs]

Does NilValue option fulfill your needs?

[jdfergason]

for this specific use case yes, it would.