Promote virEvent*Handle/Timeout to public API

Since we virEventRegisterDefaultImpl is now a public API, callers need
a way to invoke the default registered Handle and Timeout functions. We
already have general functions for these internally, so promote
them to the public API.

v2:
    Actually add APIs to libvirt.h

generator.py

@@ -398,6 +398,14 @@ skip_function = (
     'virStreamRecv', # overridden in libvirt-override-virStream.py
     'virStreamSend', # overridden in libvirt-override-virStream.py
 
+    # XXX: Skip for now, some work needed to handle Timeout/Handle callbacks
+    'virEventAddHandle',
+    'virEventRemoveHandle',
+    'virEventUpdateHandle',
+    'virEventAddTimeout',
+    'virEventRemoveTimeout',
+    'virEventUpdateTimeout',
+
     # 'Ref' functions have no use for bindings users.
     "virConnectRef",
     "virDomainRef",