Add support for infinite discrete spaces

[bvssvni]

Currently, the spaces that are available in this library are finite in size.

One idea is to use () for dimension of infinite discrete spaces.
These will enumerate arbitrarily.

Alternative is to allow arbitrary types as dimension and use identity map for counting.

[bvssvni]

An example is infinite permutations, which divides natural numbers into a group generator and the infinite identity group:

[0, 1, 2, 3] [4, 5, 6, 7, ...]