Update rcbox annotations for acquire/release functions

The accepted behaviour for reference counting functions can be described
as such:

 - acquire: takes a pointer to a memory area and returns the same
   pointer with its reference count increased; this means that the
   returned value's ownership is fully transfered from the callee
   to the caller
 - release: takes a pointer to a memory area and drops the reference
   count; this means that the caller transfers the ownership of the
   argument to the callee

These annotations are mostly meant for documentation purposes: high
level language bindings are unlikely to use them, as they have their own
reference counting semantics on top of GLib's own, and they should not
expose this API to their own consumers.
8 jobs for refcount-box in 8 minutes and 47 seconds (queued for 9 seconds)
Status Job ID Name Coverage
  Build
passed #59464
cross-android_api21_arm64

00:00:48

passed #59465
cross-android_api28_arm64

00:01:07

passed #59466
cross-mingw64

00:01:24

passed #59463
fedora-x86_64

00:02:56

canceled #59469
freebsd-11 allowed to fail
freebsd-11-x86_64

passed #59467
win32
msys2-mingw32

00:07:56

passed #59468
win32
vs2017-x64

00:06:15

 
  Coverage
passed #59470
coverage

00:00:50

69.9%