feat: configure cursor distance from viewport edges

TODO.md

@@ -1,6 +1,6 @@
-- [ ] make all buffers (including pickers) scrolls the window when the cursor reaches a certain threshold. setting could something like "distance from frame edges", and the value could be an integer or none:
-	- "none" would mean "always keep the cursor in the center of the frame" (i.e. scroll the viewport whenever the cursor moves to a different line)
-	- an integer value would be the distance from the edge of the viewport that the cursor must hit before the viewport begins to scroll. a value of 0 means the viewport scrolls only right before the cursor would otherwise have left the viewport; a value greater than half the width of the viewport behaves similarly to "none" (at least until the viewport is resized to support that range in a meaningful way).
+- [ ] add option to highlight trailing whitespace (off by default)
+- [ ] add option to put characters at certain whitespace characters (off by default)
+	- whitespace kind -> character map should be configurable.
 - [ ] github/gitlab/gitea integration (probably requries authentication with github)
 	- github pr picker (floating window)
 	- three tabs: open, closed, all