docs: Clarify handling of 64-bit integer literals with g_object_new()
docs: Clarify handling of 64-bit integer literals with g_object_new()

As with `g_variant_new()` (or any varargs function which takes integer
literals of differing widths), callers need to be careful to ensure
their integer literals have the right width.

Tweak the documentation for `g_object_new()`, `g_object_set()` and
`g_object_get()` to clarify this. The documentation for `g_object_get()`
shows that it is not subject to the same caveats, since it operates on
pointers.

Signed-off-by: Philip Withnall <withnall@endlessm.com>

Closes: #833

endlessm/glib,endlessm/glib,endlessm/glib,endlessm/glib,endlessm/glib