(new): JSON HTML escaping control

- add Formatter.JSONEscapeHTML and SetJSONEscapeHTML to let JSON writers preserve HTML-sensitive characters when needed while keeping escaping enabled by default.
- switch JSON output to json.Encoder, preserve existing Print/Println newline semantics, and cover the new escaping behavior in tests.

formatter.go

@@ -32,9 +32,10 @@ type Formatter struct {
 	Format           string
 	MessageSeparator string
 
-	// JSONTraceBackPath
-	// If true, in traceback will be path to file, otherwise only filename.
-	JSONTraceBackPath  bool
+	// JSONTraceBackPath enables full file paths in formatted traceback fields.
+	JSONTraceBackPath bool
+	// JSONEscapeHTML controls whether JSON output escapes HTML-sensitive characters.
+	JSONEscapeHTML     bool
 	TimeStampFormat    string
 	TraceBackFormat    string
 	TraceBackSeparator string
@@ -57,6 +58,7 @@ var DefaultTextFormatter = &Formatter{
 // DefaultJsonFormatter is the default formatter used by JSON writers.
 var DefaultJsonFormatter = &Formatter{
 	Format:           "%m",
+	JSONEscapeHTML:   true,
 	MessageSeparator: " ",
 	TimeStampFormat:  RFC3339,
 	ColorOutput:      false,
@@ -67,6 +69,7 @@ func NewFormatter() *Formatter {
 	return &Formatter{
 		Format:             DefaultTextFormatter.Format,
 		MessageSeparator:   DefaultTextFormatter.MessageSeparator,
+		JSONEscapeHTML:     true,
 		TimeStampFormat:    DefaultTextFormatter.TimeStampFormat,
 		TraceBackFormat:    DefaultTextFormatter.TraceBackFormat,
 		TraceBackSeparator: DefaultTextFormatter.TraceBackSeparator,
@@ -87,6 +90,18 @@ func (f *Formatter) SetMessageSeparator(separator string) *Formatter {
 	return f
 }
 
+// SetJSONTraceBackPath enables or disables full file paths in formatted traceback fields.
+func (f *Formatter) SetJSONTraceBackPath(set bool) *Formatter {
+	f.JSONTraceBackPath = set
+	return f
+}
+
+// SetJSONEscapeHTML enables or disables HTML escaping in JSON output.
+func (f *Formatter) SetJSONEscapeHTML(escape bool) *Formatter {
+	f.JSONEscapeHTML = escape
+	return f
+}
+
 // SetTimeStampFormat sets the strftime-like format used for timestamps.
 func (f *Formatter) SetTimeStampFormat(format string) *Formatter {
 	f.TimeStampFormat = format