Release build optimizations: (#155)

* lto = "fat"
* codegen-units=1

Author: molpopgen

Cargo.toml

@@ -11,6 +11,10 @@ repository = "https://github.com/tskit-dev/tskit-rust"
 
 # See more keys and their definitions at https://doc.rust-lang.org/cargo/reference/manifest.html
 
+[profile.release]
+lto = "fat"
+codegen-units=1
+
 [dependencies]
 thiserror = "1.0"
 libc = "0.2.81"