Move fish-rust to project root

src/wutil/errors.rs

@@ -0,0 +1,12 @@
+#[derive(Debug, Copy, Clone, PartialEq, Eq)]
+pub enum Error {
+    // The value overflowed.
+    Overflow,
+
+    // The input string was empty.
+    Empty,
+
+    // The input string contained an invalid char.
+    // Note this may not be returned for conversions which stop at invalid chars.
+    InvalidChar,
+}