Added `cradle::remove_rvalue_reference`.

cradle/type_traits/remove_rvalue_reference.hpp: Newly added.
test/type_traits/remove_rvalue_reference_compile.cpp: Newly added.
Added `cradle::as_const`.

* jamroot: Added aliases for `src/utility` and `src/functional`.
* cradle/config/config.hpp: Newly added.
* cradle/utility/as_const.hpp: Newly added.
* src/utility/jamfile: Newly added.
* test/utility/jamfile: Newly added.
* test/utility/as_const_run.cpp: Newly added.
Added `CRADLE_SIMPLE_AUTO_FORWARD_RETURN`.

* cradle/utility/simple_auto_forward_return.hpp: Newly added.
* test/utility/simple_auto_forward_return_run.cpp: Newly added.
Added `cradle::invoke`.

* cradle/functional/invoke.hpp: Newly added.
* src/functional/jamfile: Newly added.
* test/functional/jamfile: Newly added.
* test/functional/invoke_run.cpp: Newly added.