Resolve "get pe c++14 ready"

Closes #58 (closed)

Memory Management:

• replace PtrVector with std::vector<std::unique_ptr>
• replace current iterators with wrapped versions of std::vector::iterator
• removed PtrVector
• replace manual memory management by smart pointers

API changes:

• no more base() function for iterators
• iterator::operator* now behaves like iterator::operator-> both return RigidBody