TLV Redux

Alright @adamvoncorswant, feel free to take a peek when you get a moment. Never before has there been such a test-covered parser :tada: 

FYI @linnie if you're interested. EMV stuff and all that.
Do we want to add some validation of no emptiness? Like `ValueChecks.noneEmpty`. Just to make sure the constructed object is proper before returning it to the caller?