Add more --border options

Instead of drawing the window border in Vim using an extra window,
extend the --border option so that we do can it natively.

Close #2223
Fix #2184

man/man1/fzf.1

@@ -192,6 +192,16 @@ Draw border around the finder
 .br
 .BR horizontal "  Horizontal lines above and below the finder"
 .br
+.BR vertical "    Vertical lines on each side of the finder"
+.br
+.BR top
+.br
+.BR bottom
+.br
+.BR left
+.br
+.BR right
+.br
 
 .TP
 .B "--no-unicode"