Some functions were duplicated, the only difference was a const in one
parameter. The definitions in the header were with const, so I kept
those versions.
Also, the functions in the header are pure C, so add extern "C",
this fixes issues with MSVC and the formerly duplicated functions.
Don't include the lazy precompiled.h everywhere, only what's
required for the compilation unit.
platform.h needs to be included instead to provide all essential
defines and types.
All includes use the relative path to the neo or the game
specific root.
Move all idlib related includes from idlib/Lib.h to precompiled.h.
precompiled.h still exists for the MFC stuff in tools/.
Add some missing header guards.
