Merge pull request #69 from yuqiang-yuan/item34-ffi

Item 34 done

src/SUMMARY.md

@@ -43,5 +43,6 @@
     - [第 32 条：搭建持续集成（CI）系统](./chapter_5/item32-ci.md)
 - [超出 Rust 标准](./chapter_6.md)
     - [第 33 条：考虑使库代码与 `no_std` 兼容](./chapter_6/item33-no-std.md)
+    - [第 34 条：控制跨越 FFI 边界的内容](./chapter_6/item34-ffi.md)
     - [第 35 条：优先使用bindgen而不是手动FFI映射](./chapter_6/item35-bindgen.md)
     [后记](./afterword.md)

src/chapter_4/item25-dep-graph.md

@@ -153,7 +153,7 @@ dep-graph v0.1.0
 [Item 31]: ../chapter_5/item31-use-tools.md
 [Item 32]: ../chapter_5/item32-ci.md
 [Item 33]: ../chapter_6/item33-no-std.md
-[Item 34]: https://www.lurklurk.org/effective-rust/ffi.html
+[Item 34]: ../chapter_6/item34-ffi.md
 [alternate registry]: https://doc.rust-lang.org/cargo/reference/registries.html
 [frowned upon]: https://rust-lang.github.io/rfcs/3463-crates-io-policy-update.html
 [one definition rule]: https://en.wikipedia.org/wiki/One_Definition_Rule