ru: translate navigation titles: days 3-4

[1dimir]

• Translate new msids related to navigation of days 3 and 4 sections;
• Rename to provide more context:     * Iterator -> Типаж Iterator     * IntoIterator -> Типаж IntoIterator     * FromIterator -> Типаж FromIterator
• Rename: Функции -> Небезопасные функции (Unsafe Functions)
• Mention alternatives in translator's comments;
• Mark translations brought from the Rust book;

#326