I will squash these commits when I'm done...

Author: Tyler Slabinski

doc/borrow_mut.md

@@ -61,14 +61,8 @@ This generates:
 ```rust
 # #[macro_use] extern crate derive_more;
 # #[derive(Borrow)]
+# #[borrow(forward)]
 # struct SingleFieldForward(Vec<i32>);
-# impl <__BorrowT: ?::core::marker::Sized> ::core::borrow::Borrow<__BorrowT> for
-# SingleFieldForward where Vec<i32>: ::core::borrow::Borrow<__BorrowT> {
-#    #[inline]
-#    fn borrow(&self) -> &__BorrowT {
-#        <Vec<i32> as ::core::borrow::Borrow<__BorrowT>>::borrow(&self.0)
-#    }
-# }
 impl<__BorrowMutT: ?::core::marker::Sized> ::core::borrow::BorrowMut<__BorrowMutT> for SingleFieldForward
 where
     Vec<i32>: ::core::borrow::BorrowMut<__BorrowMutT>,