Add traits for operations that change the load order

src/load_order/error.rs

@@ -0,0 +1,35 @@
+/*
+ * This file is part of libloadorder
+ *
+ * Copyright (C) 2017 Oliver Hamlet
+ *
+ * libespm is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation, either version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * libespm is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with libespm. If not, see <http://www.gnu.org/licenses/>.
+ */
+
+use error::Error;
+
+#[derive(Debug)]
+pub enum LoadOrderError {
+    PluginError(Error),
+    PluginNotFound,
+    TooManyActivePlugins,
+    InvalidPlugin(String),
+    ImplicitlyActivePlugin(String),
+}
+
+impl From<Error> for LoadOrderError {
+    fn from(error: Error) -> Self {
+        LoadOrderError::PluginError(error)
+    }
+}

src/load_order/mod.rs

@@ -17,7 +17,9 @@
  * along with libespm. If not, see <http://www.gnu.org/licenses/>.
  */
 
+mod error;
 mod readable;
+mod writable;
 mod tests;
 
 use unicase::eq;