Check statements with cargo check

[Bedis Nbiba]

The initial issue #67

Currently we don't do any check if the input is a statement, this is so the repl feels fast for those operations at least.

But still its weird when errors only appears after using an expression.

I tested cargo check and it turns out its not that slow, so its ok to use it to check each statement,

Also this behaviour should be configurable.

[Bedis Nbiba]

@fdncred I believe that #67 is now correctly fixed.