cjson_util module

Utility modules for parsing multilevel keys and validated datatypes.
Lifted and packaged from Indigo's configuration manager.
Remove incorrect comments.
Use aim_zmalloc().
Fix headers.
The lookup_path__ code can now safely mutate the input path directly.
Merge into master from pull request #27:
cjson_util module (https://github.com/floodlight/bigcode/pull/27)