Cmake install targets fixed

Use of GNUInstallDirs and other ideas borrowed from commit
119c3747bf7e0c17adf7576dc31274bfbcf2a3c1 by Laszlo Nagy
<laszlo.3.nagy@nokia.com> in https://github.com/rizsotto/Crisp.
Cmake project name changed Crisp -> crisp
kill autotools build system

Conflicts:
	CMakeLists.txt
	docs/examples/Makefile
	include/CMakeLists.txt
	include/crisp/Config/config.h.in
Kill LICENSE.TXT

After killing autoconf and Makefiles written by hand, no files are
covered by licenses different from GPLv3 any more. GPLv3 is still
bundled in file COPYING.
Simplified AUTHORS file

Now we rely on commit history at Github.
Target 'check' re-enabled

Only if llvm-lit present. Inspired by commit
525ad1badd5b27d86d75137ab069f0cc8c33ebeb by Laszlo Nagy
<laszlo.3.nagy@nokia.com> in https://github.com/rizsotto/Crisp.
LlvmLibsAndTools: cmake module

cmake/llvm-clang.cmake replaced by proper Cmake module LlvmLibsAndTools.

Many other Cmake improvements:
- Better Cmake dependencies handling for Prolog boot saved states.
- Removed requirement of library Threads.
- Better handling of required C/CXX compiler.
- Documentation of useful variables.

First 3 strategies of LlvmLibsAndTools.cmake testes in both Release and
Debug mode.

lit testing based on CMAKE_CXX_COMPILER instead of CLANG_EXECUTABLE.