Fixes #306

Allow install targets to be optionally defined

Added test files to .gitignore

Fix typo

Add support for the cleanup attribute in GCC/Clang

The new json_auto_t macro allows easy declaration of json_t types that
automatically decrement at the end of their scope.

Fixes #300

Fixes #300

Always preserve insertion order of object items

OOM crash 

and increasing hashtable order

Fixes a crash observed when there is OOM in hashtable_do_rehash

Polish API documentation

Simplify snprintf and vsnprintf checking for Visual Studio

The object_to_key_iter() example is now formatted like
json_object_foreach() and json_object_foreach(). The edited descriptions were
redundant, and the removed headers didn't add useful information.

The function signatures use "json", not "root".

Patch by Blanca Elio Rosario.

Don't crash on deeply nested values by limiting parser recursion depth

The fix limits recursion depths when parsing arrays and objects.
The limit is configurable via the `JSON_PARSER_MAX_DEPTH` setting
within `jansson_config.h` and is set by default to 2048.

Update the RFC conformance document to note the limit; the RFC
allows limits to be set by the implementation so nothing has
actually changed w.r.t. conformance state.

Reported by Gustavo Grieco.