A follow-up on a previous PR GH-41. The discussion in the forum can be
viewed at http://forum.openclonk.org/topic_show.pl?pid=33086.
Run clang-tidy (without auto, pass-by-value and using checks) to fix the
header files not modified in the previous PR.
Summary of the changes:
- C++11 member initialization.
- nullptr instead of 0 for pointers.
- override for functions declared virtual in base class.
- default trivial special member functions
Consolidate the include statements scattered across the code in accordance
with the comment in C4Include.h. The advantages are listed in the same
comment.
Furthermore, it follows llvm-include-order which is the logical
extrapolation of the project's style guideline wherever possible
(C4Include.h being the most-frequent exception).