stylistic: Crate features are subtractive rather than additive

[crackheadakira]

A minor nitpick, but according to the Cargo Book, dependencies should be additive instead of subtractive.

But the current crate has it's features set up as subtractive.

[amodm]

@crackheadakira good eye, thank you. I wish I had paid attention to this detail when creating these features. I haven't yet seen reports of an issue because of this, so will not treat this as a high priority issue. But will incorporate this when a major release is planned (because it'll be a breaking change).

I'll leave this issue open until that happens.