docs/library/builtins: Add docs for delattr and slice.

docs/library/builtins.rst

@@ -28,6 +28,11 @@ All builtin functions are described here. They are also available via
 
 .. class:: complex()
 
+.. function:: delattr(obj, name)
+
+   The argument *name* should be a string, and this function deletes the named
+   attribute from the object given by *obj*.
+
 .. class:: dict()
 
 .. function:: dir()
@@ -110,6 +115,10 @@ All builtin functions are described here. They are also available via
 
 .. function:: setattr()
 
+.. class:: slice()
+
+   The *slice* builtin is the type that slice objects have.
+
 .. function:: sorted()
 
 .. function:: staticmethod()