commands: Show server error info in browser

The main item in this commit is showing of errors with a file context when running `hugo server`.

This can be turned off: `hugo server --disableBrowserError` (can also be set in `config.toml`).

But to get there, the error handling in Hugo needed a revision. There are some items left TODO for commits soon to follow, most notable errors in content and config files.

Fixes #5284
Fixes #5290
See #5325
See #5324

releaser/releaser.go

@@ -16,7 +16,6 @@
 package releaser
 
 import (
-	"errors"
 	"fmt"
 	"io/ioutil"
 	"log"
@@ -26,6 +25,8 @@ import (
 	"regexp"
 	"strings"
 
+	"github.com/pkg/errors"
+
 	"github.com/gohugoio/hugo/helpers"
 )
 
@@ -255,7 +256,7 @@ func (r *ReleaseHandler) release(releaseNotesFile string) error {
 	cmd.Stderr = os.Stderr
 	err := cmd.Run()
 	if err != nil {
-		return fmt.Errorf("goreleaser failed: %s", err)
+		return errors.Wrap(err, "goreleaser failed")
 	}
 	return nil
 }