fix how `stack_aligned_protected_function` and its friends behave
add new internal handler details to allow for stack-based handlers with maximum performance
update `string_shim` typedef to simply be called `string_view` and use `string_view` in all public-facing APIs.
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