Add data structures section

Propose itertools and typemap.

Disclosure: I maintain itertools.

README.md

@@ -110,6 +110,11 @@ Only projects that are stable and useful to users are added. Projects that do no
 * [lifthrasiir/rust-chrono](https://github.com/lifthrasiir/rust-chrono) — [<img src="https://travis-ci.org/lifthrasiir/rust-chrono.svg?branch=master">](https://travis-ci.org/lifthrasiir/rust-chrono)
 * [rust-lang/time](https://github.com/rust-lang/time) — [<img src="https://travis-ci.org/rust-lang/time.svg?branch=master">](https://travis-ci.org/rust-lang/time)
 
+### Data structures
+
+* [bluss/rust-itertools](https://github.com/bluss/rust-itertools) — [<img src="https://travis-ci.org/bluss/rust-itertools.svg?branch=master">](https://travis-ci.org/bluss/rust-itertools)
+* [reem/rust-typemap](https://github.com/reem/rust-typemap) — [<img src="https://travis-ci.org/reem/rust-typemap.svg?branch=master">](https://travis-ci.org/reem/rust-typemap)
+
 ### Encoding
 
 * [TyOverby/bincode](https://github.com/TyOverby/bincode) — a binary encoder/decoder in Rust [<img src="https://travis-ci.org/TyOverby/bincode.svg?branch=master">](https://travis-ci.org/TyOverby/bincode)