feat(quickjs): add quickjs

from: https://crates.io/crates/quick-js

quickjs/external/quickjs-rs/libquickjs-sys/README.md

@@ -0,0 +1,32 @@
+# libquickjs-sys
+
+FFI Bindings for [quickjs](https://bellard.org/quickjs/), a Javascript engine.
+
+See the [quick](https://crates.io/crates/quickjs) crate for a high-level
+wrapper.
+
+**Embedded VERSION: 2020-07-05**
+
+## Embedded vs system
+
+By default, an embedded version of quickjs is used.
+
+If you want to use a version installed on your system, use:
+
+
+```toml
+libquickjs-sys = { version = "...", default-features = false, features = ["system"] }
+```
+
+
+## Updating the embedded bindings
+
+QuickJS sources and a pre-generated `bindings.rs` are included in the repo.
+
+They are used if the `embedded` feature is enabled.
+
+To updat the bindings, follow these steps:
+
+* (Install [just](https://github.com/casey/just))
+* Update the download URL in ./justfile
+* run `just quickjs-update`