ENH: additional HashTable emplace/insert/set methods (#1286)

- support move insert/set and emplace insertion.

  These adjustments can be used for improved memory efficiency, and
  allow hash tables of non-copyable objects (eg, std::unique_ptr).

- extend special HashTable output treatment to include pointer-like
  objects such as autoPtr and unique_ptr.

ENH: HashTable::at() method with checking. Fatal if entry does not exist.