BLI: generally improve C++ data structures

The main focus here was to improve the docs significantly. Furthermore,
I reimplemented `Set`, `Map` and `VectorSet`. They are now (usually)
faster, simpler and more customizable. I also rewrote `Stack` to make
it more efficient by avoiding unnecessary copies.

Thanks to everyone who helped with constructive feedback.

Approved by brecht and sybren.

Differential Revision: https://developer.blender.org/D7931

source/blender/blenlib/BLI_math_bits.h

@@ -23,6 +23,7 @@
  */
 
 #include "BLI_math_inline.h"
+#include "BLI_utildefines.h"
 
 #ifdef __cplusplus
 extern "C" {