stdlib: Add Result and Option types

Since the type checker sucks less now, we can think about maybe
adding some features to the language.

...At some point I'd like to have the type checker clean up
the index map.

stdlib/std/result.cl

@@ -0,0 +1,21 @@
+//! The Result type, indicating a fallible operation.
+
+pub enum Result<T, E> {
+    Ok(T),
+    Err(E),
+}
+
+impl Result {
+    pub fn is_ok(&self) -> bool {
+        match self {
+            Ok(_) => true,
+            Err(_) => false,
+        }
+    }
+    pub fn is_err(&self) -> bool {
+        match self {
+            Ok(_) => false,
+            Err(_) => true,
+        }
+    }
+}