Add tests for binary values

[nlohmann]

This PR adds tests for the binary values introduced in #1662 and fixes some subtle bugs along the way.

Closes #2082.

[nlohmann]

@OmnipotentEntity Could you please have a look? Maybe I broke something along the way. I am still not 100% sure whether the internal binary type fits as it is right now, but at least now there is better coverage to test some things.

[OmnipotentEntity]

I distinctly remember typing up a response to this thread yesterday. I guess I forgot to actually click comment. Whoops.

I clearly didn't understand SAX on my first time through, and I forgot to adjust it as I learned exactly what it was supposed to do, whoops.

Good catch on the binary comparison bug, that one is actually somewhat funny.

I don't quite understand the binary constructor fix, but what I don't understand is why I wrote that code in the first place. I was probably cribbing off of the array code, but that's entirely not necessary for a single valued function.

Tests look good to me. New features are smart additions.

[coveralls]

Coverage increased (+1.01%) to 99.841% when pulling 6014419 on issue2082 into 1de30bc on develop.