Added semantic analysis test for assignment to nested tuples
Added nested tuple syntax to type annotations; plus test cases
Added parse test for nested tupple assignment
Added test for parsing nested tuples and lists in for-statements
Added parsing of nested tuples in for statements
Added test for type inference from nested tuples to index variable of for-statement
Removed unused types field from GeneratorExpr and parse_for_index_variables
Added test for nested tuples in generator expressions
Added parsing of star expressions
Extended  star expression parser test. Created parser test for star expression in for-statement (skipped for now)
WIP semantic analysis of star expression
Extended star expression parse tests
Fixed implementation of parsing of star expressions (also in for-statements)