Make different parts of the output configurable by setting user functions

This naming convention denotes “private” functions; however, if we want to introduce more
customization, we should make these available and documented well.

org-clock-waybar.el

@@ -7,7 +7,7 @@
 ;; Keywords: org, clocking, waybar
 ;; URL: https://gitea.polonkai.eu/gergely/org-clock-waybar
 ;; Package-Version: 1.0
-;; Package-Requires: ((emacs "26.1") (org "9"))
+;; Package-Requires: ((emacs "26.1") (org-mode "9"))
 
 ;; This program is free software; you can redistribute it and/or modify
 ;; it under the terms of the GNU General Public License as published by
@@ -148,24 +148,24 @@ When nil, the percentage text will be an empty string."
 The output is in JSON format constructed in a way so Waybar can process it.
 If there is no clocked in task, alt becomes empty and text will be set to the
 value of `org-clock-waybar-not-clocked-in-text'."
-  (let* ((text-func (or (and (fboundp ('org-clock-waybar-text-function)))
+  (let* ((text-func (or 'org-clock-waybar-text-function
-                         #'org-clock-waybar-get-task-title))
+                         'org-clock-waybar-get-task-title))
          (text (funcall text-func))
-         (alt-func (or (and (fboundp ('org-clock-waybar-alt-function)))
+         (alt-func (or 'org-clock-waybar-alt-function
-                       #'org-clock-waybar-get-task-category))
+                       'org-clock-waybar-get-task-category))
          (alt (funcall alt-func))
-         (tooltip-func (or (and (fboundp ('org-clock-waybar-tooltip-function)))
+         (tooltip-func (or 'org-clock-waybar-tooltip-function
-                           #'org-clock-waybar-get-tooltip))
+                           'org-clock-waybar-get-tooltip))
          (tooltip (funcall tooltip-func))
-         (class-func (or (and (fboundp ('org-clock-waybar-class-function)))
+         (class-func (or 'org-clock-waybar-class-function
-                         #'org-clock-waybar-get-tags))
+                         'org-clock-waybar-get-tags))
          (class (funcall class-func))
          (percentage (when (fboundp 'org-clock-waybar-percentage-function)
-                       (funcall #'org-clock-waybar-percentage-function)))
+                       (funcall 'org-clock-waybar-percentage-function)))
          (output (json-new-object)))
-    (or (null text)
+    (or (null title)
-        (stringp text)
+        (stringp title)
-        (error "Text must be a string (org-clock-waybar)!"))
+        (error "Title must be a string (org-clock-waybar)!"))
     (or (null alt)
         (stringp alt)
         (error "Alt text must be a string (org-clock-waybar)!"))