Unwrap union

[domn1995]

Closes #104.

Design notes:

• Chose to implement only "unsafe" version that can throw an exception for now. The reason is because it's the most useful option with no easy alternative currently in the library.
• Decided against having Unsafe in the name due to potential confusion with the unsafe keyword and because it doesn't communicate the action being performed. Unwrap doesn't have either downside and has precedent from its usage in Rust.
• Still open to a Try() alternative that's more idiomatic C# but will let community drive that if they want it. A nullable return version might also be nice in the future as well.