Unused variable: FPs due to expressions not considered

[montyly]

If a variable is used as the length of an array, it will not be considered as used

contract C {
  uint constant X = 100;
  uint[X] array;
  function f() external{
    array[0] = 1;
  }
}

We need to document all the places that can have an expression:

• node.expression
• variable.expression
• length of an ArrayType
• ?

[montyly]

Fixed in 0ad0777