Tensor value as parameter

[marcelluethi]

Add a value type parameter to Tensor and factory methods to create a tensor.

A Float32 Tensor is created using the following pattern

val t : Tensor1[A, Float32] = Tensor.of[Float32].ones(Shape(Axis[A]->3)

and a custom type can be created using

trait Y
object Y extends Value.As[Y, Float32]
val t : Tensor1[A, Y] = Tensor.of[Y].ones(Shape(Axis[A]->3)

Note that for arithmetic operations the Value type needs to correspond. The following gives a type error

Tensor0.of[Int32](3)+Tensor0.of[Float32](3f)

Instead an explicit type cast ist needed

Tensor0.of[Int32](3)+Tensor0.of[Float32](3f).asType[Int32]