Function merklebtree::iterator::first

pub fn first<T>(btree_iterator: &mut btree_iterator<T>) -> bool where
    T: PartialEq + PartialOrd + Ord + Clone + Debug + CalculateHash, 

First moves the iterator to the first element and returns true if there was a first element in the container. If First() returns true, then first element's key and value can be retrieved by Key() and Value(). Modifies the state of the iterator