CMake support

[stokito]

The CLion IDE (IntelliJ) works normally only with CMake.
Otherwise I can't debug it.
I added the CMakeList.txt just for this case.
It doesn't work completely so you may not merge it.
Anyway the PR may be useful for others like me

[mwarning]

What does not work? It compiles for me.

[stokito]

not all features are migrated: natpmp, libcadnode etc.

[mwarning]

ah, ok. understood.

[stokito]

The Makefile has this:

ifeq ($(OS),Windows_NT)
  OBJS += build/unix.o build/windows.o
else
  OBJS += build/unix.o
endif

E.g. even for a Windows we need to compile the unix.c file. Is this correct or was made by a mistake?

[mwarning]

unix.c is need to compile on Windows since Cygwin is used.

[stokito]

so this file is anyway always added then we can move it too list of all core files

[mwarning]

Yes, that sounds like a good idea.