add cJSON, update mosquitto to 1.6.3 and update the makefile

Guo Wenxue

2019-06-24 809c78de808ed5563e9af4a56227965974ec25fa

tools/rpi_crosstool.tar.bz2 does not exist in tree 545516fb7568815073f7fc2a4badb5e624edb3dd