added adaptive weight balancing algorithm

src/balancer/mod.rs

@@ -1,4 +1,7 @@
 pub mod round_robin;
+pub mod adaptive_weight;
+pub mod least_connections;
+pub mod ip_hashing;
 
 use std::fmt::Debug;
 use std::sync::Arc;
@@ -6,4 +9,4 @@ use crate::backend::Backend;
 
 pub trait Balancer: Debug + Send + Sync + 'static {
     fn choose_backend(&mut self) -> Option<Arc<Backend>>;
-}
+}