Remove github.com/pkg/errors and replace with std library version

This is possible now that we no longer support go1.12 and brings
rclone into line with standard practices in the Go world.

This also removes errors.New and errors.Errorf from lib/errors and
prefers the stdlib errors package over lib/errors.

cmd/rc/rc.go

@@ -4,13 +4,13 @@ import (
 	"bytes"
 	"context"
 	"encoding/json"
+	"errors"
 	"fmt"
 	"io/ioutil"
 	"net/http"
 	"os"
 	"strings"
 
-	"github.com/pkg/errors"
 	"github.com/rclone/rclone/cmd"
 	"github.com/rclone/rclone/fs"
 	"github.com/rclone/rclone/fs/config/flags"
@@ -163,16 +163,16 @@ func doCall(ctx context.Context, path string, in rc.Params) (out rc.Params, err
 	if loopback {
 		call := rc.Calls.Get(path)
 		if call == nil {
-			return nil, errors.Errorf("method %q not found", path)
+			return nil, fmt.Errorf("method %q not found", path)
 		}
 		_, out, err := jobs.NewJob(ctx, call.Fn, in)
 		if err != nil {
-			return nil, errors.Wrap(err, "loopback call failed")
+			return nil, fmt.Errorf("loopback call failed: %w", err)
 		}
 		// Reshape (serialize then deserialize) the data so it is in the form expected
 		err = rc.Reshape(&out, out)
 		if err != nil {
-			return nil, errors.Wrap(err, "loopback reshape failed")
+			return nil, fmt.Errorf("loopback reshape failed: %w", err)
 		}
 		return out, nil
 	}
@@ -182,12 +182,12 @@ func doCall(ctx context.Context, path string, in rc.Params) (out rc.Params, err
 	url += path
 	data, err := json.Marshal(in)
 	if err != nil {
-		return nil, errors.Wrap(err, "failed to encode JSON")
+		return nil, fmt.Errorf("failed to encode JSON: %w", err)
 	}
 
 	req, err := http.NewRequestWithContext(ctx, "POST", url, bytes.NewBuffer(data))
 	if err != nil {
-		return nil, errors.Wrap(err, "failed to make request")
+		return nil, fmt.Errorf("failed to make request: %w", err)
 	}
 
 	req.Header.Set("Content-Type", "application/json")
@@ -197,7 +197,7 @@ func doCall(ctx context.Context, path string, in rc.Params) (out rc.Params, err
 
 	resp, err := client.Do(req)
 	if err != nil {
-		return nil, errors.Wrap(err, "connection failed")
+		return nil, fmt.Errorf("connection failed: %w", err)
 	}
 	defer fs.CheckClose(resp.Body, &err)
 
@@ -211,19 +211,19 @@ func doCall(ctx context.Context, path string, in rc.Params) (out rc.Params, err
 			bodyString = err.Error()
 		}
 		bodyString = strings.TrimSpace(bodyString)
-		return nil, errors.Errorf("Failed to read rc response: %s: %s", resp.Status, bodyString)
+		return nil, fmt.Errorf("Failed to read rc response: %s: %s", resp.Status, bodyString)
 	}
 
 	// Parse output
 	out = make(rc.Params)
 	err = json.NewDecoder(resp.Body).Decode(&out)
 	if err != nil {
-		return nil, errors.Wrap(err, "failed to decode JSON")
+		return nil, fmt.Errorf("failed to decode JSON: %w", err)
 	}
 
 	// Check we got 200 OK
 	if resp.StatusCode != http.StatusOK {
-		err = errors.Errorf("operation %q failed: %v", path, out["error"])
+		err = fmt.Errorf("operation %q failed: %v", path, out["error"])
 	}
 
 	return out, err
@@ -240,7 +240,7 @@ func run(ctx context.Context, args []string) (err error) {
 		for _, param := range params {
 			equals := strings.IndexRune(param, '=')
 			if equals < 0 {
-				return errors.Errorf("no '=' found in parameter %q", param)
+				return fmt.Errorf("no '=' found in parameter %q", param)
 			}
 			key, value := param[:equals], param[equals+1:]
 			in[key] = value
@@ -251,7 +251,7 @@ func run(ctx context.Context, args []string) (err error) {
 		}
 		err = json.Unmarshal([]byte(jsonInput), &in)
 		if err != nil {
-			return errors.Wrap(err, "bad --json input")
+			return fmt.Errorf("bad --json input: %w", err)
 		}
 	}
 	if len(options) > 0 {
@@ -268,7 +268,7 @@ func run(ctx context.Context, args []string) (err error) {
 	if out != nil && !noOutput {
 		err := rc.WriteJSON(os.Stdout, out)
 		if err != nil {
-			return errors.Wrap(err, "failed to output JSON")
+			return fmt.Errorf("failed to output JSON: %w", err)
 		}
 	}
 
@@ -279,7 +279,7 @@ func run(ctx context.Context, args []string) (err error) {
 func list(ctx context.Context) error {
 	list, err := doCall(ctx, "rc/list", nil)
 	if err != nil {
-		return errors.Wrap(err, "failed to list")
+		return fmt.Errorf("failed to list: %w", err)
 	}
 	commands, ok := list["commands"].([]interface{})
 	if !ok {