add practice projects

practices/hello-package/.gitignore

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+/target

practices/hello-package/Cargo.lock

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+# This file is automatically @generated by Cargo.
+# It is not intended for manual editing.
+version = 3
+
+[[package]]
+name = "hello-package"
+version = "0.1.0"

practices/hello-package/Cargo.toml

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+[package]
+name = "hello-package"
+version = "0.1.0"
+edition = "2021"
+
+# See more keys and their definitions at https://doc.rust-lang.org/cargo/reference/manifest.html
+
+[dependencies]

practices/hello-package/Readme.md

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+## Hello Package
+A practice project used in [Crate and Module](https://practice.rs/crate-module/crate.html) chapter.
+
+This project will guide us to create a package with a binary crate and several library crates in it.
+
+The project structure is as below:
+```shell
+.
+├── Cargo.lock
+├── Cargo.toml
+├── Readme.md
+├── src
+│   ├── back_of_house.rs
+│   ├── front_of_house
+│   │   ├── hosting.rs
+│   │   ├── mod.rs
+│   │   └── serving.rs
+│   ├── lib.rs
+│   └── main.rs
+```

practices/hello-package/src/back_of_house.rs

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+use crate::front_of_house;
+pub fn fix_incorrect_order() {
+    cook_order();
+    front_of_house::serving::serve_order();
+}
+
+pub fn cook_order() {}

practices/hello-package/src/front_of_house/hosting.rs

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+pub fn add_to_waitlist() {}
+
+pub fn seat_at_table() -> String {
+    String::from("sit down please")
+}
+

practices/hello-package/src/front_of_house/mod.rs

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+pub mod hosting;
+pub mod serving;

practices/hello-package/src/front_of_house/serving.rs

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+pub fn take_order() {}
+
+pub fn serve_order() {}
+
+pub fn take_payment() {}
+
+// Maybe you don't want the guest hearing the your complaining about them
+// So just make it private
+fn complain() {} 

practices/hello-package/src/lib.rs

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+mod front_of_house;
+mod back_of_house;
+
+pub use crate::front_of_house::hosting;
+
+pub fn eat_at_restaurant() -> String {
+    front_of_house::hosting::add_to_waitlist();
+    
+    back_of_house::cook_order();
+
+    String::from("yummy yummy!")
+}

practices/hello-package/src/main.rs

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+fn main() {
+    assert_eq!(hello_package::hosting::seat_at_table(), "sit down please");
+    assert_eq!(hello_package::eat_at_restaurant(),"yummy yummy!");
+}