Improve error handling and code formatting

[alexlnkp]

• Handle ParseIntError on-the-spot during argument parsing. Use unwrap_or_else instead of unwrap().
• Use into() instead of to_string() on &str values in get_updates()

[coffebar]

Thank you for participating, but please, I would like to ask you:

• do not spam with commits,
• do not make a pull request for code formatting,
• configure the IDE for proper code formatting,
• justify the changes why they are needed, do not make commits that do not relate to the pull request

If you want this changes, create a new PR, name it "Add options validation", check your formatting (cargo fmt is ok if you don't have normal IDE or PDE) create a commit with only this feature. Name commit feature: add options validation