add extend motions, color cursor in select mode

src/cursor.rs

@@ -83,6 +83,36 @@ impl Cursor {
 			self.head -= self.head % 4;
 		}
 	}
+	
+	pub fn extend_to_next_word(&mut self, max: usize) {
+		if self.head == max { return }
+		
+		if self.head.is_multiple_of(4) { // at the beginning of a word
+			self.head = (self.head + 4).min(max);
+		} else {
+			self.head = self.head.next_multiple_of(4).min(max);
+		}
+	}
+	
+	pub fn extend_to_next_end(&mut self, max: usize) {
+		if self.head == max { return }
+		
+		if self.head % 4 == 3 { // at the end of a word
+			self.head = (self.head + 4).min(max);
+		} else {
+			self.head = ((self.head + 1).next_multiple_of(4) - 1).min(max);
+		}
+	}
+	
+	pub const fn extend_to_previous_beginning(&mut self) {
+		if self.head == 0 { return }
+		
+		if self.head.is_multiple_of(4) { // at the beginning of a word
+			self.head -= 4;
+		} else {
+			self.head -= self.head % 4;
+		}
+	}
 }
 
 mod tests {