Add compiler support for followings (unless otherwise stated, all applicable only to int type):
local variable declaration
arithmetic expression involving only binary operators
println method that takes String or int type argument
(nested) ifelse statements
while and do while loops
for loop with the form for (init; cond; update) {}
condition expression involved in if/else if/while/for can only have int or boolean literal, and can support all logical operators except logical not (!)
Tests will be added in another PR to avoid huge PR and ease process of reviewing
inttype):printlnmethod that takesStringorinttype argumentifelsestatementswhileanddo whileloopsforloop with the formfor (init; cond; update) {}if/else if/while/forcan only haveintor boolean literal, and can support all logical operators except logical not (!)