refactor api package comments

* use encoding/json for comment parsing

* refactor by moving loop code to an UnmarshalJSON

* use a preallocated array and indices to maintain order while using
  goroutines again, this was removed a while ago

* use new struct in comment.hbs and contextComment.hbs

* rewriteUrl partial to reduce rimgo-specific code in api

* move RenderError into pages package to avoid import cycle between render and utils

render/helpers.go

@@ -1,10 +1,19 @@
 package render
 
-import "github.com/mailgun/raymond/v2"
+import (
+	"time"
+
+	"codeberg.org/rimgo/rimgo/utils"
+	"github.com/dustin/go-humanize"
+	"github.com/mailgun/raymond/v2"
+)
 
 func (r *renderer) registerHelpers() {
 	funcmap := map[string]any{
-		"noteq": noteq,
+		"noteq":         noteq,
+		"ifNonZeroTime": ifNonZeroTime,
+		"relTime":       relTime,
+		"rewriteUrl":    rewriteUrl,
 	}
 	raymond.RegisterHelpers(funcmap)
 }
@@ -15,3 +24,19 @@ func noteq(a, b any, options *raymond.Options) any {
 	}
 	return ""
 }
+func ifNonZeroTime(v any, options *raymond.Options) any {
+	if v.(time.Time).IsZero() {
+		return ""
+	}
+	return options.Fn()
+}
+func relTime(date time.Time) string {
+	return humanize.Time(date)
+}
+func rewriteUrl(link string) string {
+	r, err := utils.RewriteUrl(link)
+	if err != nil {
+		panic(err)
+	}
+	return r
+}