Refer to the json-c library as per their examples.

Not using -I makes more sense to me, but it appears that some distributions
put the headers in different locations, and all the example code refers only
to json.h, so we'll follow suit...

Also link against the correct library.
Use built-in linking rules (with its own variables).
Merge branches 'build-implicit-link' and 'build-jsonc' into integrate

Conflicts:
	cpp/Makefile