json-glib: convert to meson build

json-glib: convert to meson build

Note that meson flags for gobject introspection and gtk-doc
appear to be non-standardized; going forward we should devise
a common way to deal with it.

gettext inherit is removed, as there is no equivalent functionality
in meson; NLS bits are always built and installed.

Signed-off-by: Alexander Kanavin <alexander.kanavin@linux.intel.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>