This commit enables compile-time warnings displayed whenever a deprecated
API header is included, and adjusts the existing #include directives
accordingly.
Issue #1987
To better support non-blocking terminal components, let the
'Terminal::Session::write()' function return the number of bytes
actually written.
Fixes#2240
This patch changes the top-level directory layout as a preparatory
step for improving the tools for managing 3rd-party source codes.
The rationale is described in the issue referenced below.
Issue #1082
