Remove -Wimplicit-fallthrough warning

Fix code to work without exceptions

fix cmake script overwriting compiler path

This fixes #2343

Fix fallthrough warning

Fix lexer to properly cope with repeated comments

Fix name of Homebrew formula in documentation

Fix a bug due to missing overloads in ordered_map container

fix typo

cmake: install pkg-config file relative to current_binary_dir

Fixed installation of pkg-config file on other than Ubuntu

When the testsuite is enabled, the "cmake_add_subdirectory" test
adds a second copy of the project into the build configuration, and the
project files are installed twice.

This becomes super problematic when it tries to install a file from
CMAKE_BINARY_DIR which is only available in CMAKE_CURRENT_BINARY_DIR
and bombs out with the following error message:

```
[...]
-- Installing: <DESTDIR>/usr/lib/cmake/nlohmann_json/nlohmann_jsonTargets.cmake
CMake Error at test/cmake_add_subdirectory/nlohmann_json/cmake_install.cmake:73 (file):
  file INSTALL cannot find
  "......./nlohmann-json/builddir/test/cmake_add_subdirectory/nlohmann_json.pc":
  No such file or directory.
Call Stack (most recent call first):
  test/cmake_add_subdirectory/cmake_install.cmake:47 (include)
  test/cmake_install.cmake:49 (include)
  cmake_install.cmake:94 (include)
```

distributions.
Signed-off-by: Vitaly Zaitsev <vitaly@easycoding.org>

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