This is not a move to c++17. If the compiler happens to have support
for c++17 namespace scope resolution, they have been kind enough to
backport it to gnu++14. This limits our support for really old c++14
compilers, but that was limited anyway. GCC 6.1 and clang 3.6 tested.
* To benefit from the precompiled-header (PCH) it MUST provide "the first C token."
Advantages:
Never worry about the include stack again. Remember, this means one less thing
for random module developers, community people learning C++, and new developers
to deal with. It should reduce the learning curve and barrier for participation.
Disadvantages:
Makes overall compilation a bit slower, especially without any additional
work to improve it again. There are several opportunities, places where the
PCH is probably being ignored, etc that can be addressed.
* librb is no longer a separately configured subproject.
* charybdis is now a standalone directory with a binary.
* Include path layout now requires a directory ircd/ rb/ etc.
