Rewrite all throwing methods to return Result<Value, Error>

[timburks]

Swift 5 added a standard Result enum that represents function results that can include errors. This is more concise and seems preferable to try/catch handling.

Should we update this library to use Result instead of throw (and bump the release number to 0.6)?

cc @0xced it looks like you've done this already: 0xced@a25ec65

[0xced]

Indeed, I already started to work on this. I'll submit a pull request when it's ready.

[dcow]

@0xced is this something you'd still submit if bumped or have you moved on to other things?

[0xced]

I still have pending work on my result branch that I have not even committed. It was almost two years ago, it may not even compile… But if you're interested, I can commit and push those changes so that someone else can take over.