atkmisc: Deprecate atkmisc

Also include it on the documentation to clearly state that
is deprecated.

https://bugzilla.gnome.org/show_bug.cgi?id=652798
doc: updating new symbol section on documentation

It also updates Since on several symbols, in order
to report from which stable release it became available
instead of exactly which unstable one.
atkobject: improve documentation for AtkObject::property-change

https://bugzilla.gnome.org/show_bug.cgi?id=644747
doc: improve atkutil documentation