create structs lib, mimics tuple lib, but implements Tuple.

This allows for operator overloading. It will make it significantly easier to write code for Tuple objects.

structs/Cargo.toml

@@ -0,0 +1,10 @@
+[package]
+name = "structs"
+version = "0.1.0"
+authors = ["Jon Janzen <jonjanzen@me.com>"]
+edition = "2018"
+
+# See more keys and their definitions at https://doc.rust-lang.org/cargo/reference/manifest.html
+
+[dependencies]
+approx = "0.4"