refactor(scrollbar): use variable names over unnamed pair content

examples/example.rs

@@ -119,7 +119,7 @@ fn run_app<B: Backend>(terminal: &mut Terminal<B>, mut app: App) -> std::io::Res
                         .title("Tree Widget")
                         .title_bottom(format!("{:?}", app.state)),
                 )
-                .experimental_scrollbar_margin((1, 1))
+                .experimental_scrollbar_margin(1, 1)
                 .experimental_scrollbar(Some(
                     Scrollbar::new(ScrollbarOrientation::VerticalRight)
                         .begin_symbol(None)

src/lib.rs

@@ -133,8 +133,8 @@ where
 
     /// See [`experimental_scrollbar`](Self::experimental_scrollbar)
     #[must_use]
-    pub const fn experimental_scrollbar_margin(mut self, margin: (u16, u16)) -> Self {
+    pub const fn experimental_scrollbar_margin(mut self, begin: u16, end: u16) -> Self {
-        self.scrollbar_margin = margin;
+        self.scrollbar_margin = (begin, end);
         self
     }