Add functions

src/lib.rs

 pub struct ThreadPool;
 
 impl ThreadPool {
-    
+    pub fn new(size: usize) -> ThreadPool {
+        assert!(size > 0);
+        ThreadPool
+    }
+
+    pub fn execute<F>(&self, f: F)
+        where F: FnOnce() + Send + 'static {
+
+        }
 }