Fixing a couple of minor bugs, and adding a few tests.

Makefile

build.json

src/core/json/json_reader.c

src/core/json/json_string.c

src/core/json/json_writer.c

test/core/json/json_rewrite.c

test/core/json/json_test.c

test/core/json/rewrite_test_input.json

test/core/json/rewrite_test_output_condensed.json

test/core/json/rewrite_test_output_indented.json

tools/run_tests/tests.json