args was derived from list, but cpp_function::dispatcher sends a tuple to it->impl (line #346 and #392 in pybind11.h). As a result args::size() and args::operator[] don't work at all. On my mac args::size() returns -1. Making args a subclass of tuple fixes it.
This modification taps into some newer C++14 features (if present) to
generate function signatures considerably more efficiently at compile
time rather than at run time.
With this change, pybind11 binaries are now *2.1 times* smaller compared
to the Boost.Python baseline in the benchmark. Compilation times get a
nice improvement as well.
Visual Studio 2015 unfortunately doesn't implement 'constexpr' well
enough yet to support this change and uses a runtime fallback.
