added variadic_results, to return a variable number of arguments to Lua
added variadic_results and as_results
added improved function examples (for multiple results and split overloading out)
added tests for variadics
added tests for C++17 utilities
added a forwarding header
added a specific `unsafe_function` header
added and improved documetation pages
add better handling for `readonly` to prevent bugs from `const`-ifying the return value of a member variable (e.g., unexpected copy semantics)
add more tests and add a few more handlers for new readonly type
fix simple_usertype_metatable's handling of newindex and index when not at the top level