Some day we will have ANSI C compatibility... This change doesn't make
the API backwards incompatible because uint32_t was only used in flags
to json_dump*() and the flags are meant to be used only by ORing
constants and macro output, and actually currently only JSON_INDENT
can be used.
Constructors are described more clearly and return values on error
situations more compehensively. Also add an example of the object
iteration protocol.
All pointer arguments are now tested for NULL. json_string() now also
tests that strdup() succeeds. This is to ensure that no NULL values
end up in data structures.
Also desribe the different sources of errors in documentation.
