Improve error handling + docs

[guzman-raphael]

• Convert error handling to enumeration approach Convert error handling to masked enumeration approach
• Apply similar message highlighting as before
• Add API docs
• Make return type for parse_annotation_path more readable
• In save_file, skip creating directory path as opposed to raising error if no parent
• Improve clippy reason doc in get_type_name
• Reduce scope of expect_used clippy exception
• Remove temporary clippy exceptions for docs
• Add notes about generating docs HTML site and coverage report HTML site

Fix #25
Fix #20

[Synicix]

Looks good merging