func AddEncoder(format string, encfunc EncoderFunc) {
	encoders[format] = encfunc
}
/*
AddEncoder installs an encoder for a given format.

AddEncoder("json", func(w io.Writer) Encoder { return json.NewEncoder(w) })
mt, err := Parse("application/json")
encoder, err := mt.Encoder(someWriter)
package mediatype
import (
	"bytes"
	"fmt"
	"io"
)
var encoders = make(map[string]EncoderFunc)
type EncoderFunc func(w io.Writer) Encoder
type Encoder interface {
	Encode(v interface{}) error
}