Add speed test script

Author: schungx

README.md

@@ -33,7 +33,7 @@ Standard features
 -----------------
 
 * Simple language similar to JavaScript+Rust with [dynamic](https://rhai.rs/book/language/dynamic.html) typing.
-* Fairly efficient evaluation (1 million iterations in 0.14 sec on a single-core 2.6 GHz Linux VM).
+* Fairly efficient evaluation - 1 million iterations in 0.14 sec on a single-core 2.6 GHz Linux VM running [this script](https://github.com/rhaiscript/rhai/blob/main/scripts/speed_test.rhai).
 * Tight integration with native Rust [functions](https://rhai.rs/book/rust/functions.html) and [types](https://rhai.rs/book/rust/custom-types.html), including [getters/setters](https://rhai.rs/book/rust/getters-setters.html), [methods](https://rhai.rs/book/rust/methods.html) and [indexers](https://rhai.rs/book/rust/indexers.html).
 * Freely pass Rust values into a script as [variables](https://rhai.rs/book/language/variables.html)/[constants](https://rhai.rs/book/language/constants.html) via an external [`Scope`](https://rhai.rs/book/engine/scope.html) - all clonable Rust types are supported; no need to implement any special trait. Or tap directly into the [variable resolution process](https://rhai.rs/book/engine/var.html).
 * Built-in support for most common [data types](https://rhai.rs/book/language/values-and-types.html) including booleans, [integers](https://rhai.rs/book/language/numbers.html), [floating-point numbers](https://rhai.rs/book/language/numbers.html) (including [`Decimal`](https://crates.io/crates/rust_decimal)), [strings](https://rhai.rs/book/language/strings-chars.html), [Unicode characters](https://rhai.rs/book/language/strings-chars.html), [arrays](https://rhai.rs/book/language/arrays.html) (including packed [byte arrays](https://rhai.rs/book/language/blobs.html)) and [object maps](https://rhai.rs/book/language/object-maps.html).