Better Error Handling and Error Messages

[sunmy2019]

Feature Proposed

I want to improve the quality of error messages and reduce the use of panic.

1. convert unwrap() to return anyhow::Error with informative contexts.
2. convert unwrap() to expect(...) for deadly scenarios.
3. remove unwrap() when it can be proved with pattern matching.

Use Case
This would increase its usability as a library and convey clearer messages to the users.

Known pitfalls
potentially increase binary size