- cleaning up implementation of type_list::{index_of|contains|skip|flatten}
- adding type_list::checked_index_of
- adding tests for type_list::checked_indef_of
- cleaning up implementation of type_map::find
- adding type_map::get
- cleaning up implementation of tuple_tags::index_of
- replacing variadic_union::list with variadic_union::tidy_list
- adding get_member_type::{name|name_type|names|names_type|ids|ids_type}