[inferno-ml] Make asTensor* and asArray* functions polymorphic

[ngua]

Currently we only allow double values to be converted back and forth between tensors, which I don't think is ideal since we've already introduced the scalar typeclass to represent scalar values that can be used with tensors.

So this makes asArray1 and asTensor1 (and their nested equivalents) polymorphic for any scalar value.

Examples:

asTensor*

let is : array of int = 1..5 in
ML.asTensor1 ML.#float is

// Tensor Float [5] [ 1.0000   ,  2.0000   ,  3.0000   ,  4.0000   ,  5.0000   ]

let bs = [[ #true, #true ], [ #false, #false ]] in
ML.asTensor2 ML.#bool bs

// Tensor Bool [2,2] [[ 1,  1], [ 0,  0]]

asArray*

let t = ML.ones ML.#int [3, 3] in
ML.asArray2 t

// [[1,1,1],[1,1,1],[1,1,1]]

let t = ML.ones ML.#bool [3, 2, 1] in
ML.asArray3 t

// [[[#true],[#true]],[[#true],[#true]],[[#true],[#true]]]