Unmarshalling of pointers is not working correctly for number types

[jangraefen]

When using the UnmarshalRequest function, an error occures if a non-nil values is unmarshalled for a number type.
It seems that conversion can not be done on a reflection level for pointer types.

Considering the following snippet:

type reqInput struct {
	field *int `lambda:"query.field"`
}

// ...

var input reqInput
lmdrouter.UnmarshalRequest(req, false, &input)

The following error will be produced:

reflect.Value.Convert: value of type *string cannot be converted to type *int: string

The root cause seems to be inside the decoder in the unmarshalField function:

lmdrouter/decoder.go

Line 193 in fb89207

valueField.Set(reflect.ValueOf(&val).Convert(typeField))

I will create a PR which will fix this behaviour and add a naiv test case.