Implement basic frontend-engine interaction

Use a Flask-based Python server as an adapter to the engine's
stdin-stdout inferface.

rs/src/main.rs

@@ -1,7 +1,19 @@
+use std::io::BufRead;
 mod board;
 mod ui;
 
-fn main() {
-    let board = board::Board::new();
-    println!("{}", board.to_string());
+fn main() -> Result<(), ()> {
+    let mut board = board::Board::new();
+    board.reset();
+    let stdin = std::io::stdin();
+    let mut input_lines = stdin.lock().lines();
+    loop {
+        match input_lines.next() {
+            None => break Ok(()),
+            Some(line) => match &line.unwrap()[..] {
+                "get_state" => println!("{}", board.to_string()),
+                _ => break Err(()),
+            },
+        }
+    }
 }