notably, test normal + single + generated + Lua 5.3.5 only once,
then only run the runtime_test and compile_test for normal for all other permutations to help increase text matrix throughput
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