Extend primitive types with small fixed-size arrays

[pavel-kirienko]

I found it to be often useful to have small fixed-size arrays for representation of arbitrary arrays and matrices without the array prefix:

• uavcan.primitive.array.Real16x2 ... Real16x9
• uavcan.primitive.array.Real32x2 ... Real32x9
• uavcan.primitive.array.Real64x2 ... Real64x9

That would be 24 new types in total.

@thirtytwobits should we add this to the core set?

[thirtytwobits]

I'm not a huge fan. This seems like syntactic sugar that the integrator should provide themselves.

[pavel-kirienko]

The reason I want these types in the standard set is that they are generic and thus useful for building simple vendor-agnostic interfaces. An integrator could surely provide equivalent definitions but it would result in a slightly less composable solution.