func (api *Client) MarkIMChannel(channel, ts string) (err error) {
	return api.MarkIMChannelContext(context.Background(), channel, ts)
}
MarkIMChannel sets the read mark of a direct message channel to a specific point
package slack
import (
	"context"
	"net/url"
	"strconv"
)
type imChannel struct {
	ID string `json:"id"`
}
type imResponseFull struct {
	NoOp          bool      `json:"no_op"`
	AlreadyClosed bool      `json:"already_closed"`
	AlreadyOpen   bool      `json:"already_open"`
	Channel       imChannel `json:"channel"`
	IMs           []IM      `json:"ims"`
	History
	SlackResponse
}
type IM struct {
	Conversation
	IsUserDeleted bool `json:"is_user_deleted"`
}
func (api *Client) imRequest(ctx context.Context, path string, values url.Values) (*imResponseFull, error) {
	response := &imResponseFull{}
	err := api.postMethod(ctx, path, values, response)
	if err != nil {
		return nil, err
	}
	return response, response.Err()
}
func (api *Client) CloseIMChannel(channel string) (bool, bool, error) {
	return api.CloseIMChannelContext(context.Background(), channel)
}
func (api *Client) CloseIMChannelContext(ctx context.Context, channel string) (bool, bool, error) {
	values := url.Values{
		"token":   {api.token},
		"channel": {channel},
	}
	response, err := api.imRequest(ctx, "im.close", values)
	if err != nil {
		return false, false, err
	}
	return response.NoOp, response.AlreadyClosed, nil
}
func (api *Client) OpenIMChannel(user string) (bool, bool, string, error) {
	return api.OpenIMChannelContext(context.Background(), user)
}
func (api *Client) OpenIMChannelContext(ctx context.Context, user string) (bool, bool, string, error) {
	values := url.Values{
		"token": {api.token},
		"user":  {user},
	}
	response, err := api.imRequest(ctx, "im.open", values)
	if err != nil {
		return false, false, "", err
	}
	return response.NoOp, response.AlreadyOpen, response.Channel.ID, nil
}