Feature: support "natural" maps

[mihaiav]

It seems that map types are not supported. E.g. map[interface{}]interface{} or map[string]string. Is this the expected behaviour?

Play

package main

import (
	"fmt"
	"github.com/go-playground/form"
	"net/url"
	"reflect"
)

func main() {
	dec := form.NewDecoder()

	req := url.Values{"a": []string{"a"}, "b": []string{"b"}, "c": []string{"1"}}

	v := map[interface{}]interface{}{
		"a": "",
		"b": "",
		"c": 0,
	}

	expected := map[interface{}]interface{}{
		"a": "a",
		"b": "b",
		"c": 1,
	}
	if err := dec.Decode(&v, req); err != nil {
		panic(err)
	}
	if !reflect.DeepEqual(v, expected) {
		fmt.Printf("expected\n %#v\n received\n %#v", expected, v)
	}
}