add G motion and up/down/left/right

src/cursor.rs

@@ -1,5 +1,3 @@
-use crate::BYTES_PER_LINE;
-
 #[derive(Debug, Default, PartialEq, Eq)]
 pub struct Cursor {
 	pub head: usize,
@@ -33,8 +31,9 @@ impl Cursor {
 		self.tail = self.head;
 	}
 	
-	pub fn clamp(&mut self, scroll_position: usize, window_rows: usize) {
-		let max_row = scroll_position + window_rows * BYTES_PER_LINE - 1;
+	// TODO: in visual mode, should only clamp head
+	pub fn clamp(&mut self, scroll_position: usize, screen_size: usize) {
+		let max_row = scroll_position + screen_size - 1;
 		
 		self.head = self.head.clamp(scroll_position, max_row);
 		self.tail = self.tail.clamp(scroll_position, max_row);