0.2.0

Added:

• Added get overloads thats consume the Key&&.

Changed:

• Changed the Value that can be created by a factory. It now must use
  std::enable_shared_from_this (or equivalently implement
  shared_from_this()).

• Changed how values are stored in the factory cache. They are now stored as
  const Value* and not as std::weak_ptr<Value> anymore.

• Changed required C++ version. Now we need at least C++17.

Performance:

• Improved get which now uses only a single lookup and create call.