Add etude::as
Add etude::forward
Add test for etude::forward
Fix etude::forward
Fix etude::move's behavior
Split etude::move from forward.hpp
Add vector-initialization test to as
Add constexpr test
Add further tests for etude::as
Fix typo
Add ETUDE_ENABLE_IF
Modify etude::as using ETUDE_ENABLE_IF
Fix missing include
Cosmetics
Merge branch 'add-utility' into develop