How to run a sample example?  #175

use hash_db::Hasher;
use reference_trie::{RefTrieDBMut, RefTrieDB};
use trie_db::DBValue;
use keccak_hasher::KeccakHasher;
use memory_db::*;

fn main() {
    let mut memdb = MemoryDB::<KeccakHasher, HashKey<_>, _>::default();
    let mut root = Default::default();
    RefTrieDBMut::new(&mut memdb, &mut root).insert(b"foo", b"bar").unwrap();
    let t = RefTrieDB::new(&memdb, &root);
    assert!(t.contains(b"foo").unwrap());
    assert_eq!(t.get(b"foo").unwrap().unwrap(), b"bar".to_vec());
}