Add more options to Scrollbar (#1174)

* Make `Scrollbar` accept a table for its options

* Add `force_status`, `{expanded,shrinked}_size` options to `Scrollbar`

* Add `Scrollbar:set_forced_status`

* Add `config.force_scrollbar_status` to force `DocView` scrollbars status

data/core/view.lua

@@ -59,8 +59,8 @@ function View:new()
   self.scroll = { x = 0, y = 0, to = { x = 0, y = 0 } }
   self.cursor = "arrow"
   self.scrollable = false
-  self.v_scrollbar = Scrollbar("v", "e")
-  self.h_scrollbar = Scrollbar("h", "e")
+  self.v_scrollbar = Scrollbar({direction = "v", alignment = "e"})
+  self.h_scrollbar = Scrollbar({direction = "h", alignment = "e"})
   self.current_scale = SCALE
 end