Merge pull request #1651 from sakurawald/highlight-line-color-option

feature: add option for highlight line-color.

src/highlight-line.lisp

@@ -1,8 +1,14 @@
 (in-package :lem-core)
 
 (define-editor-variable highlight-line nil)
+(define-editor-variable highlight-line-color nil)
 
 (defun highlight-line-color ()
+  (alexandria:if-let ((color (variable-value 'highlight-line-color)))
+    color
+    (guess-highlight-line-color)))
+
+(defun guess-highlight-line-color ()
   (when (background-color)
     (let ((color (parse-color (background-color))))
       (multiple-value-bind (h s v)