Rust Minor improvement to binary-trees 3
Tuple in TreeNode is replaced by left and right references to nodes. It's correct, because left or right node can be missing in real world application, and is faster by about 0.05s at 21 depth.
The command to build is (same as previous): /opt/src/rust-1.33.0/bin/rustc -C opt-level=3 -C target-cpu=core2 -C lto -C codegen-units=1 -L /opt/src/rust-libs binarytrees.rs -o binarytrees.rust-3.rust_run