pratt.py: better comments
add nud to Node
NONE supports bools, eval and repr
Str supports GetItem
append operator (<<<)
Arrays support iteration
Interpreter.Iter
support forloop in grammar
missing ForLoop class
fix typo error message in Call.eval
fix (Get|Set)Attr/Item mess
add comments for debug purposes
arrays.ls: fix return value
tests/func_triv.ls: fix return value
run-tests.sh: run all available tests
Added more tests
new file:   tests/for_loop.ls