Updated std::Option, std::Either and std::Result

- Made naming schemes consistent between Option, Result and Either
- Changed Options Add implementation to work like the maybe monad (return None if any of the inputs is None)
- Removed duplicate Option::get and renamed all related functions to use the term `unwrap` instead

src/libstd/task/mod.rs

@@ -926,7 +926,7 @@ fn test_named_task() {
         t.name(~"ada lovelace");
         do t.spawn {
             do with_task_name |name| {
-                assert!(name.get() == "ada lovelace");
+                assert!(name.unwrap() == "ada lovelace");
             }
         }
     }