No need Cargo.toml but still respect it if it's there

Just got some info that you can compile rust code without _Cargo.toml_ using `rustc`. Also, command `cargo rustc` will respect _Cargo.toml_ ⎝✧ᴥ✧⎠

future plans


Seems I can replace `cargo build` with `cargo rustc`?
Also, using `--emit` flags and pipe it as a return value seems to be a good idea. Some projects need to import different `.rs` file which mean there will be multiple compilation. This cause `out-dir` to be rewrited multiple times :disappointed:

#### Good References
https://github.com/rust-lang/cargo/issues/595
https://doc.rust-lang.org/rustc/codegen-options/index.html
https://doc.rust-lang.org/cargo/reference/external-tools.html
https://doc.rust-lang.org/cargo/reference/unstable.html#out-dir
https://journal.zeyi.fan/2019/08/20/announce-cargo-play.html