Add new iterator implementation and some NULL-pointer safety

Additional explanatory comments

New json_object_object_get_ex() method protects itself against null pointers
and invalid objects being passed in.

New lh_table_lookup_ex() method protects itself against null pointers
and invalid objects being passed in.

Changing root name of library to json-c, and also the
directory where header files are installed to .../jsdon-c/*.

This avoids clashes with other implementations of JSON libraries.

Change the resize check from "count > size" to "count >= size" to avoid a
potential infinite loop with high load factors and a full hash table.

Fix a typo in the string represenations of the json_tokener_error_depth error (s/to deep/too deep/)

Change the resize check from "count > size" to "count >= size" to avoid a
potential infinite loop with high load factors and a full hash table.

Renaming the boolean type to json_bool in json_object.h

Fix a typo in the string represenations of the json_tokener_error_depth error (s/to deep/too deep/)

In building large systems, there are often clashes over the
preferred base type to use for bool/boolean. At least one
experience has been with a 3rd party proprietary library which
can not be changed. In that case, boolean was a synonym for
unsigned char and used widely in packed structures.

Add documentation for the json_tokener_parse_ex() function.

As part of this create a public json_config.h with a custom define to
decide whether to include inttypes.h to avoid conflicting with other
projects config.h header.