Remove the last character in the render buffer on backspace

src/main.rs

@@ -263,11 +263,17 @@ impl FramebufferWriter {
 
 impl fmt::Write for FramebufferWriter {
     fn write_char(&mut self, c: char) -> fmt::Result {
+        if c == '\u{8}' {
+            self.out_string.pop();
+        } else {
             self.out_string.push(c);
+        }
         Ok(())
     }
     fn write_str(&mut self, s: &str) -> core::fmt::Result {
-        self.out_string.push_str(s);
+        for c in s.chars() {
+            self.write_char(c)?;
+        }
         Ok(())
     }
 }