implement blueprint creation, placement, saving and loading

src/marble_engine/board.rs

@@ -1,3 +1,5 @@
+use std::ops::Add;
+
 use crate::{draw_scaled_texture, Textures};
 
 use super::tile::*;
@@ -50,6 +52,16 @@ impl From<Vector2> for Pos {
 	}
 }
 
+impl Add for Pos {
+	type Output = Self;
+	fn add(self, rhs: Self) -> Self::Output {
+		Self {
+			x: self.x + rhs.x,
+			y: self.y + rhs.y,
+		}
+	}
+}
+
 #[derive(Debug, Clone)]
 pub struct Board {
 	rows: Vec<Vec<Tile>>,