This only attaches the parsed linked lists to the items passed to
parse_object and parse_array.

This replaces the bit fiddling involved with calculating a new buffer
size by just multiplying the required length by two, paving the way to a
complete switch to size_t at a later point in time.

Introduces a preprocessor directive that aborts the compilation if the
version numbers in the header don't match with the numbers in the c
file.

Add new type cJSON_Invalid

This sets the type of an item only if parsing was successful.

This means that in case of failure, the item's type will remain to be
cJSON_Invalid.

This assigns the macro cJSON_Invalid to 0.

This fixes a double free that happens when calling cJSON_Delete on an
item that has been used by parse_string and it failed parsing the
string.

The double free happens, because parse_string frees an alias of
item->valuestring, but doesn't set item->valuestring to NULL.

Thanks @rrvirtual for the suggestion.

Introduce the cunity testing framework

Enabling this flag enables AddressSanitizer and
UndefinedBehaviorSanitizer

Test parsing and printing example files

git-subtree-dir: tests/unity
git-subtree-split: 1782bab0bacd349a45bc215ff91f082912cd7a64

Simplify some code and improve correctness

This might cause slight changes in behavior, but it shouldn't break
anything that is not already broken (for example the original macro
could either return a double, or an integer or whatever depending on if
object is NULL or not.)

Replaces the hand written floating point parser with the C library
implementation.