package/rapidjson: switch to CMake

package/rapidjson: switch to CMake

Upcoming Kodi v18 depends on RapidJSON and detects it by using pkg-conf:
https://github.com/xbmc/xbmc/blob/master/cmake/modules/FindRapidJSON.cmake#L13

Currently our package installs only the header files, but RapidJSON.pc
is also needed. Luckily this can be fixed by switching to CMake which
does the job, also add configure options to disable the CMake build of
executables.

Signed-off-by: Bernd Kuhls <bernd.kuhls@t-online.de>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>