add `scripts` directory to EXTRA_DIST

add jansson_* to shared library exports

Update apiref.rst

add MinGW build guideline and tips to disable building docs

add changes since v2.12

Format code with clang-format

Set ColumnLimit to 90, remove AllowShortCaseLabelsOnASingleLine.

fix issue #441: remove strtod definition in strconv.c

Add json_object_update_new, json_object_update_existing_new and json_object_update_missing_new

Recursive object update

fix issue #426: fix pipe function in MinGW

fix issue #481

fix issue #453:update FindSphinx.cmake to better align with find sphinx package.

add note for non-blocking file descriptor used for json_loadfd

fix typo & add negative test case for test_equal_complex

Support merging values nested within objects. For instance, merging:

    {
	"foo": 1,
	"bar": {
	    "baz": 2
	}
    }

with

    {
	"bar": {
	    "baz": 3
	}
    }

results in

    {
	"foo": 1,
	"bar": {
	    "baz": 3
	}
    }

instead of overwriting the value for the bar key.