...fix RapidJSON dependency, remove features from CMake

I've now implemented in Meson all the remaining features that were in
CMake, like Cppcheck and Doxygen documentation. I've also removed almost
all the non-essential features from CMake, like building examples,
documentation, code coverage, the install target, Cppcheck, and tarball
generation. This should help with maintainability, while preserving
testability, following @kiplingw and @dennisjenkins75 main concerns.

Cppcheck is not ran by default, but it is a build target; you can run it
with `meson compile -C builddir cppcheck`.

I've also made some little fixes and tweaks:

Fixed RapidJSON
dependency, as it was previously declared only as a dependency of the
run_rest_description example, while used in
include/pistache/thirdparty/serializer/rapidjson.h.

Updated CMakeLists, replacing the old Include(Dart) with the newer
Include(CTest), and also adding messaging suggesting the user to install
RapidJSON and GoogleTest on their system rather than building them from
source.

Fixed a "small" issue in meson.build, replacing add_global_arguments
with add_project_arguments, since the former can't be used in
subprojects and can cause build failures for users.