Implicit items/pairs invocations

If the for loop expression e does not denote an iterator and the for loop has exactly 1 variable, the for loop expression is rewritten to items(e); ie. an items iterator is implicitly invoked:

for x in [1,2,3]: echo x

If the for loop has exactly 2 variables, a pairs iterator is implicitly invoked.

Symbol lookup of the identifiers items/pairs is performed after the rewriting step, so that all overloads of items/pairs are taken into account.