Add support for serializing to, and de-serializing from, JSON, as
specified in RFC 8259. Format is automatically detected for input,
and can be specified explicitly for output. The default format remains
XML.

As part of this change, generic prop_object_{internalize,externalize}()
functions are provided, and the "_with_format" flavor allows the output
format to be specified. Previous array- and dictionary-specific routines
remain for backwards compatibility.

branches: 1.9.12;
Improvements to the problib(3) API:

==> Provide a much more complete set of setters and getters for different
value types in the prop_array_util(3) and prop_dictionary_util(3)
functions.

==> Overhaul the prop_data(3), prop_number(3), and prop_string(3) APIs
to be easier to use and less awkwardly named, Deprecate the old
awkward names, and produce link-time warnings when they are referenced.

==> Deprecate mutable prop_data(3) and prop_string(3) objects. The old
APIs that support them still exist, but will now produce link-time
warnings when used.

==> When the new prop_string(3) API is used, strings are internally
de-duplicated as a memory footprint optimization.

==> Provide a rich set of bounds-checked gettter functions in and a
corresponding set of convenience setters in the prop_number(3) API.

==> Add a new prop_bool_value(3) function that is equivalent to
prop_bool_true(3), but aligned with the new "value" routines in
prop_data(3), prop_string(3), and prop_number(3).

branches: 1.8.34;
Use Lk macro when dealing with URLs. While here update or remove some
dead URL links. Another part of PR/29238.

branches: 1.7.6;
- Implement prop_{array,dictionary}_copyout(), based on
prop_{array,dictionary}_copyout_ioctl().
- Implement prop_{array,dictionary}_recv_syscall(), which
takes as parameter the pref we got from kernel and internalize it,
and unmaps the buffer prop_{array,dictionary}_copyout() mapped for us.
- add a prop_{array,dictionary}_send_syscall() for symetry, which is
an alias to prop_{array,dictionary}_externalize_to_pref()

Discussed on tech-kern@ and tech-userlevel@

New sentence, new line.

branches: 1.5.8;
Convert TNF licenses to new 2 clause variant

branches: 1.4.10;
Xref prop_dictionary_util(3) and prop_send_ioctl(3).

Drop trailing whitespace.

Change prop_number_t to store a uint64_t, rather than a uintmax_t. No
ABI change, and we ought to explicitly state that this is a fixed-width
type, since that what it needs to be for binary plist support.

Initial commit of proplib, a library for manipulating property lists and
converting to/from an XML external representation (based on Apple XML
property lists). Works in the kernel and user space.