Add static token lifetime

src/token/mod.rs

@@ -29,3 +29,6 @@ pub trait Lifetime {
 
 pub use self::bearer::Bearer;
 mod bearer;
+
+pub use self::statik::Static;
+mod statik;

src/token/statik.rs

@@ -0,0 +1,8 @@
+use super::Lifetime;
+
+/// A static, non-expiring token.
+pub struct Static;
+
+impl Lifetime for Static {
+    fn expired(&self) -> bool { false }
+}