Start new Error structure in state_processing

eth2/state_processing/src/macros.rs

@@ -0,0 +1,8 @@
+#[macro_use]
+macro_rules! ensure {
+    ($condition: expr, $result: ident) => {
+        if !$condition {
+            return Err(Error::Invalid(Invalid::$result));
+        }
+    };
+}