Struct Point conversion to tuple (ixmilia#47)

Added tuple conversion for struct Point for one liner extraction of its
inner data by introducing method "tuple".

This change is just for convenience to downstream user in getting
coordinates like the examples below:

```rust
let (x, _, z) = p.tuple();
let (_, y, z) = p.tuple();
let (x, y, _) = p.tuple();
```

src/point.rs

@@ -36,4 +36,24 @@ impl Point {
 
         Ok(())
     }
+
+    pub fn tuple(&self) -> (f64, f64, f64) {
+        (self.x, self.y, self.z)
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    /// Tests whether tuple conversion works as intended and Point doesn't get consumed.
+    #[test]
+    fn tuple_conversion_case() {
+        let p = Point::new(1.0, 1.0, 1.0);
+        let t: (f64, f64, f64) = p.tuple();
+
+        dbg!(&p);
+        dbg!(&t);
+        assert_eq!(t, p.tuple())
+    }
 }