More samples

Finally fixed the problem with assignment in the right hand side of an "and" making the variable nilable afterwards and, when in an "if"'s condition, not being nil.

better havlak code

add Havlak benchmark

Some AST name refactors: Ident -> Path, IdentUnion -> Union, FunTypeSpec -> Fun, Arg#type_restriction -> Arg#restriction

Set Array's default capacity to 3 instead of 16. Also, when using an array literal use the element count as the capacity.