Improve error handling

[mclang]

Problem

Error handling is mix of everything found from the examples.

Solution

1. Check that plain unwrap() is not used haphazardly - use except instead.
2. Improve panic! usage where necessary.
3. Get rid of unnecessary panics by using ok_or_else, map_err and possibly with anyhow crate.
4. Improve error handling: Practical Guide to Error Handling
5. Check also You're probably misusing unwrap in Rust...