Assignment tests for check 3a.
Assignability tests for check 3b.
Added decltype tests for check 3c.
Answer files for check 3c.
If and while tests for check 4.
Function-call tests for check 5.
Return statement tests for check6a.
Added tests for check6a; fixed check 5 to match.
Added tests for check 6b.
Added tests for check 6c.
holy shit