Switch String Processing to Regex

I replaced all the raw string manipulation with Regular Expressions.

There's a lot of little changes everywhere. The CLI has a new flag, instantiation is different, a bunch of From traits are now TryFrom to indicate they can fail, which of course necessitates error handling...

There's also a couple more tangential changes. The readme has new examples, and I changed the lints in CI to add one allow.

If the changes to the tests weren't a clue, this is a breaking change.

Closes #7 (closed).