feat(solutions): add camel-case/rust/function

challenges/camel-case/solutions/rust/function/Cargo.lock

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+# This file is automatically @generated by Cargo.
+# It is not intended for manual editing.
+version = 3
+
+[[package]]
+name = "rust_application"
+version = "1.0.0"

challenges/camel-case/solutions/rust/function/Cargo.toml

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+[package]
+name = "rust_application"
+version = "1.0.0"
+edition = "2021"
+
+[dependencies]

challenges/camel-case/solutions/rust/function/README.md

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+# camel-case/rust/function
+
+Created by [@Divlo](https://github.com/Divlo) on 4 January 2023.

challenges/camel-case/solutions/rust/function/src/main.rs

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+use std::io;
+
+pub fn capitalize(string: &str) -> String {
+    let mut character = string.chars();
+    match character.next() {
+        None => String::new(),
+        Some(value) => value.to_uppercase().collect::<String>() + character.as_str(),
+    }
+}
+
+pub fn camel_case(string: &str) -> String {
+    let mut result: Vec<String> = Vec::new();
+    let words: Vec<&str> = string.trim().split_whitespace().collect();
+    for (index, word) in words.iter().enumerate() {
+        let is_first_word = index == 0;
+        if is_first_word {
+            result.push(word.to_string());
+        } else {
+            let word = capitalize(&word);
+            result.push(word);
+        }
+    }
+    return result.join("");
+}
+
+fn main() {
+    let mut string = String::new();
+    io::stdin()
+        .read_line(&mut string)
+        .expect("Failed to read `stdin` line.");
+    println!("{}", camel_case(&string));
+}