Add check for template aliases.
Implement variadic template factories. Fixes #140.
Don't include <tuple> inside a namespace
Add factory_base::add_default_edge(node, node_token)
Make node::get_token public and const
factory_helpers.h: Use remove<> in constructed::type
Use remove<> in push_type and pull_type
factory_helpers.h: Use move semantics if supported
Remove support for var. templates without rvalue references

It does not seem like any of the compilers we target support variadic
templates without also supporting rvalue references, so we can make the
code simpler by removing a supported configuration that does not occur
in practice.
Edit gen_factory_helpers_inl.py
Regenerate factory_helpers.inl
Only print the "Too many steps" error once