(new): prepare v2.1.0 release

- add custom LogLevel constructors and richer color configuration
- support ANSI, 256-color, RGB, and text attributes on LogLevel
- introduce clearer preferred APIs such as NewLogger and SetName
- preserve backward compatibility with deprecated wrappers for v2.0.1 APIs
- restore legacy ColorStringBuilder signatures as compatibility wrappers
- fix newline separator handling in Println-style output
- add tests for color precedence, deprecated aliases, and LogLevel attributes
- update GoDoc and bilingual README documentation

time_format.go

@@ -91,6 +91,7 @@ var strftimeToGoRules = []rule{
 	{"%r", "03:04:05 PM"},
 }
 
+// StrftimeToGo converts a strftime-like layout into a Go time layout.
 func StrftimeToGo(format string) string {
 	var out strings.Builder
 
@@ -121,6 +122,7 @@ func StrftimeToGo(format string) string {
 	return out.String()
 }
 
+// GoToStrftime converts a Go time layout into an approximate strftime-like layout.
 func GoToStrftime(format string) string {
 	format = strings.ReplaceAll(format, "2006", "%Y")
 	format = strings.ReplaceAll(format, "06", "%y")