Allow customizing scrollbar of the preview window via --scrollbar=xy

CHANGELOG.md

@@ -5,6 +5,15 @@ CHANGELOG
 ------
 - Added color name `preview-border` and `preview-scrollbar`
 - Added new border style `block` which uses [block elements](https://en.wikipedia.org/wiki/Block_Elements)
+- `--scrollbar` can take two characters, one for the main window, the other
+  for the preview window
+- Putting it altogether
+  ```sh
+  fzf-tmux -p 80% --padding 1,2 --preview 'bat --style=plain --color=always {}' \
+      --color 'bg:#222233,bg+:#333344,gutter:#222233,border:#111122,scrollbar:#ffaa00' \
+      --color 'preview-bg:#332233,preview-border:#222222,preview-scrollbar:#00aaff' \
+      --preview-window 'border-block' --border block --scrollbar '▌▐'
+  ```
 - Bug fixes and improvements
 
 0.40.0