Vendor things

third-party/vendor/overload/README.md

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+<p align="center"><img width="460" src="https://github.com/danaugrs/overload/blob/master/logo.png"></p>
+<p align="center">
+  <a href="https://docs.rs/overload"><img src="https://docs.rs/overload/badge.svg"/></a>
+  <a href="https://crates.io/crates/overload"><img src="https://img.shields.io/crates/v/overload.svg"/></a>
+</p>
+
+Provides a macro to simplify operator overloading. See the [documentation](https://docs.rs/overload/) for details and supported operators.
+
+## Example
+
+```rust
+extern crate overload;
+use overload::overload;
+use std::ops; // <- don't forget this or you'll get nasty errors
+
+#[derive(PartialEq, Debug)]
+struct Val {
+    v: i32
+}
+
+overload!((a: ?Val) + (b: ?Val) -> Val { Val { v: a.v + b.v } });
+```
+
+The macro call in the snippet above generates the following code:
+
+```rust
+impl ops::Add<Val> for Val {
+    type Output = Val;
+    fn add(self, b: Val) -> Self::Output {
+        let a = self;
+        Val { v: a.v + b.v }
+    }
+}
+impl ops::Add<&Val> for Val {
+    type Output = Val;
+    fn add(self, b: &Val) -> Self::Output {
+        let a = self;
+        Val { v: a.v + b.v }
+    }
+}
+impl ops::Add<Val> for &Val {
+    type Output = Val;
+    fn add(self, b: Val) -> Self::Output {
+        let a = self;
+        Val { v: a.v + b.v }
+    }
+}
+impl ops::Add<&Val> for &Val {
+    type Output = Val;
+    fn add(self, b: &Val) -> Self::Output {
+        let a = self;
+        Val { v: a.v + b.v }
+    }
+}
+``` 
+
+We are now able to add `Val`s and `&Val`s in any combination:
+
+```rust
+assert_eq!(Val{v:3} + Val{v:5}, Val{v:8});
+assert_eq!(Val{v:3} + &Val{v:5}, Val{v:8});
+assert_eq!(&Val{v:3} + Val{v:5}, Val{v:8});
+assert_eq!(&Val{v:3} + &Val{v:5}, Val{v:8});
+```