chore: add vendor dependencies for kauma build

vendor/itoa/README.md

@@ -0,0 +1,59 @@
+itoa
+====
+
+[<img alt="github" src="https://img.shields.io/badge/github-dtolnay/itoa-8da0cb?style=for-the-badge&labelColor=555555&logo=github" height="20">](https://github.com/dtolnay/itoa)
+[<img alt="crates.io" src="https://img.shields.io/crates/v/itoa.svg?style=for-the-badge&color=fc8d62&logo=rust" height="20">](https://crates.io/crates/itoa)
+[<img alt="docs.rs" src="https://img.shields.io/badge/docs.rs-itoa-66c2a5?style=for-the-badge&labelColor=555555&logo=docs.rs" height="20">](https://docs.rs/itoa)
+[<img alt="build status" src="https://img.shields.io/github/actions/workflow/status/dtolnay/itoa/ci.yml?branch=master&style=for-the-badge" height="20">](https://github.com/dtolnay/itoa/actions?query=branch%3Amaster)
+
+This crate provides a fast conversion of integer primitives to decimal strings.
+The implementation comes straight from [libcore] but avoids the performance
+penalty of going through [`core::fmt::Formatter`].
+
+See also [`ryu`] for printing floating point primitives.
+
+*Version requirement: rustc 1.36+*
+
+[libcore]: https://github.com/rust-lang/rust/blob/b8214dc6c6fc20d0a660fb5700dca9ebf51ebe89/src/libcore/fmt/num.rs#L201-L254
+[`core::fmt::Formatter`]: https://doc.rust-lang.org/std/fmt/struct.Formatter.html
+[`ryu`]: https://github.com/dtolnay/ryu
+
+```toml
+[dependencies]
+itoa = "1.0"
+```
+
+<br>
+
+## Example
+
+```rust
+fn main() {
+    let mut buffer = itoa::Buffer::new();
+    let printed = buffer.format(128u64);
+    assert_eq!(printed, "128");
+}
+```
+
+<br>
+
+## Performance (lower is better)
+
+![performance](https://raw.githubusercontent.com/dtolnay/itoa/master/performance.png)
+
+<br>
+
+#### License
+
+<sup>
+Licensed under either of <a href="LICENSE-APACHE">Apache License, Version
+2.0</a> or <a href="LICENSE-MIT">MIT license</a> at your option.
+</sup>
+
+<br>
+
+<sub>
+Unless you explicitly state otherwise, any contribution intentionally submitted
+for inclusion in this crate by you, as defined in the Apache-2.0 license, shall
+be dual licensed as above, without any additional terms or conditions.
+</sub>