Underline highlighted lines in ANSI theme (#1985)

* Underline highlighted lines in ANSI theme

* add test for ansi highlight underline, fix underscore in plain

src/printer.rs

@@ -463,6 +463,10 @@ impl<'a> Printer for InteractivePrinter<'a> {
         let highlight_this_line =
             self.config.highlighted_lines.0.check(line_number) == RangeCheckResult::InRange;
 
+        if highlight_this_line && self.config.theme == "ansi" {
+            self.ansi_style.update("^[4m");
+        }
+
         let background_color = self
             .background_color_highlight
             .filter(|_| highlight_this_line);
@@ -649,6 +653,11 @@ impl<'a> Printer for InteractivePrinter<'a> {
             writeln!(handle)?;
         }
 
+        if highlight_this_line && self.config.theme == "ansi" {
+            self.ansi_style.update("^[24m");
+            write!(handle, "\x1B[24m")?;
+        }
+
         Ok(())
     }
 }