[RFC] Retiring [t] for arrays

[supercooldave]

The notation for array types [t] conflicts somewhat with the notation for type parameters, leading to types like the following [Maybe[[t]]]. After a little practice, one naturally overcomes any possible confusion, but I think for uniformity, wouldn't it be better to deprecate [t] and replace it by Array[t], allowing, for example, Array[Maybe[Array[t]]].

Perhaps this depends on the much awaited PR from Gustav (@glundi).