Refactor out Crd3D and Crd2D to use df::coord and df::coord2d

[realSquidCoder]

Fixes #205

[NicksWorld]

This is casting a int16_t* to int*.

[ab9rf]

I'm going to stand here in opposition to the entire idea behind this PR. df::coord and df::coord3d are garbage types and we should use them only to the extent possible required to remain compatible with DF. In code that is doing its own manipulation of 2-tuples and 3-tuples of ints representing coordinate vectors, we should absolutely not use df::coord because this could result in slower code. The compiler is going to use 32-bit math under the hood anyway, and constantly forcing narrowing and widening conversions is of no benefit. The only time you should be using int16_t is when memory bandwidth is an issue, and that's not the case for singleton or small lists of 3-tuples which is the overwhelming use case here.

I would instead recommend keeping these types mostly as is, and add the required constructors and cast operators to the Crd2D and Crd3D types so that they are implicitly interconvertible with df::coord objects, to the extent this is useful. If it is needed to represent "invalid" values, add an isValid boolean or wrap in std::optional (which does the same thing and adds a convenient API)

[realSquidCoder]

im completely in agreement with this. this PR broke more than it fixed.

[realSquidCoder]

This is not gonna happen