std::function in Conversion System

[ardasener]

The conversion system originally used ConversionFunctor pointers which had the following problems:

• Required manual memory allocation on our part
• Made the destructor complicated (since the user could pass multiple copies of the same objects we had to be careful about double deletion)
• Required all converters to conform to this style

The new system uses std::function objects instead as a result:

• The user can define converters in many different ways (functions, static member functions, lambda expressions etc.)
• No need to manage the memory on our side