statuslinevisibility: Add TOGGLE

Example of usage:
    :noremap <silent> <F8> :js statusline.setVisibility(statusline.setVisibility.TOGGLE)<CR>

Author: SammysHP

common/content/statusline.js

@@ -131,6 +131,7 @@ const StatusLine = Module("statusline", {
             this.setVisibility.UPDATE = 0; // Apply current configuration
             this.setVisibility.SHOW   = 1; // Temporarily show statusline
             this.setVisibility.HIDE   = 2; // Temporarily hide statusline
+            this.setVisibility.TOGGLE = 3; // Cycle through all three modes (auto, visible, hidden)
 
             this.setVisibility.contentSeparator = highlight.get('ContentSeparator').value;
             this.setVisibility.isVisible = true;
@@ -197,6 +198,14 @@ const StatusLine = Module("statusline", {
                     hideStatusline();
                 }
                 break;
+
+            case sv.TOGGLE:
+                switch (mode) {
+                    case "auto":    options["statuslinevisibility"] = "visible"; break;
+                    case "visible": options["statuslinevisibility"] = "hidden";  break;
+                    case "hidden":  options["statuslinevisibility"] = "auto";    break;
+                }
+                break;
         }
     },