Allow identifier and expressions when referencing an array index

[blapaz]

Currently only a number can be used to reference an array index, so the below code would have issues at line array[i]. However, this should be allowed, along with expressions array[(i - 1)].

i = 4	

while (i > 0)
{
  array[i] = array[(i - 1)]
  i = i - 1
}