The concept type traits are renamed for consistency,
and consolidated into a single header file <beast/core/type_traits.hpp>
A new section, Core Concepts, is added to the documentation describing all
of the core utility classes and functions. This also includes a complete
explanation and sample program describing how to write asynchronous initiation
functions and their associated composed operations.
fix#242
* Add public constructors
* Add handler_ptr::empty()
* Add handler_ptr::element_type
* Remove make_handler_ptr free function
* Compiler error if element_type is an array type
* handler_ptr::get() returns nullptr if no object is owned
Vinnie Falco