Fix error C3688 when compiling on Visual Studio 2015

Add FALLTHRU comment to handle GCC7 warnings.

Fix compilation without C-99 option

fix doc in tokener header file

Also, there's no need to worry about output consistency here, since it'll be
 different anyway due to different pointer values.

Improve json_object -> string performance

Hawciz pointed out that the previous commit modifies the public
interface of printbuf. Per his suggestion, sprintbuf() was restored
and a new pair of macros was added that wraps printbuf_memappend().

Using a wrapper macro instead of modifying sprintbuf() also reduces
function call overhead, bringing total performance gains to
approximately 400%.

Removes variadic prints for ~3x performance improvement.

bugfix: floating point representaion without fractional part

closes https://github.com/json-c/json-c/issues/278

json_pointer: extend setter & getter with printf() style arguments

Signed-off-by: Alexandru Ardelean <ardeleanalex@gmail.com>

Signed-off-by: Alexandru Ardelean <ardeleanalex@gmail.com>

Signed-off-by: Alexandru Ardelean <ardeleanalex@gmail.com>

These include support for printf() style args for path.

Adds support for calling with 'json_pointer_getf(obj, &res, "/foo/%d/%s", 0, bar)'
style args.

Makes it easier for doing more dynamic stuff/magic, without
needing to use vasprintf() externally.

Signed-off-by: Alexandru Ardelean <ardeleanalex@gmail.com>

Signed-off-by: Alexandru Ardelean <ardeleanalex@gmail.com>

Revert "compat/strdup.h: move common compat check for strdup() to own…

This reverts commit aaba8c1080.

This commit breaks builddir != srcdir build, but, more importantly, it
also adds a dependency on a header, "config.h", which is not installed
and it's supposed to be private — since it's generated at configuration
time and it's not meant to be used by projects compiling against a
library.

json_pointer: add first revision based on RFC 6901

Signed-off-by: Alexandru Ardelean <ardeleanalex@gmail.com>

I got this on Mac OS X at least.
Not sure if it shows up in other envs

error:
```
strerror_override.c:53:13: error: incompatible redeclaration of library function 'strerror' [-Werror,-Wincompatible-library-redeclaration]
const char *strerror(int errno_in)
```

Signed-off-by: Alexandru Ardelean <ardeleanalex@gmail.com>

Signed-off-by: Alexandru Ardelean <ardeleanalex@gmail.com>

Signed-off-by: Alexandru Ardelean <ardeleanalex@gmail.com>

Allows for compilation with CMake on macOS

Json object set xxx