cleanup, use struct update syntax

examples/unix_timestamp.v

@@ -4,7 +4,6 @@ import structlog
 fn main() {
 	// Initialize logger with edited timestamp.
 	log := structlog.new(
-		// timestamp_format: .unix
 		timestamp: structlog.Timestamp{
 			format: .unix
 		}

structlog.v

@@ -96,9 +96,8 @@ pub fn (r Record) append(field ...Field) Record {
 	mut fields_orig := unsafe { r.fields }
 	fields_orig << field
 	return Record{
-		channel: r.channel
+		...r
-		level:   r.level
+		fields: &fields_orig
-		fields:  &fields_orig
 	}
 }
 
@@ -110,9 +109,8 @@ pub fn (r Record) prepend(field ...Field) Record {
 	mut new_fields := unsafe { field }
 	new_fields << r.fields
 	return Record{
-		channel: r.channel
+		...r
-		level:   r.level
+		fields: new_fields
-		fields:  new_fields
 	}
 }