python 3.7 support

- replace `raise StopIteration` by `return`
https://www.python.org/dev/peps/pep-0479/#examples-of-breakage
- replace time.clock() by time.time() since we don't really care which time it is but the latter still works

pyffi/object_models/xml/__init__.py

@@ -101,13 +101,13 @@ def __init__(cls, name, bases, dct):
             # which takes care of the class creation
             cls.logger.debug("Parsing %s and generating classes."
                              % xml_file_name)
-            start = time.clock()
+            start = time.time()
             try:
                 parser.parse(xml_file)
             finally:
                 xml_file.close()
             cls.logger.debug("Parsing finished in %.3f seconds."
-                             % (time.clock() - start))
+                             % (time.time() - start))
 
 
 class FileFormat(pyffi.object_models.FileFormat, metaclass=MetaFileFormat):

pyffi/object_models/xml/enum.py

@@ -95,7 +95,7 @@ def __next__(cls):
             cls.__i += 1
             return (cls._enumkeys[cls.__i-1], cls._enumvalues[cls.__i-1])
         else:
-            raise StopIteration
+            return
 
     def __getitem__(cls, key):
         if key in cls._enumkeys:

pyffi/object_models/xsd/__init__.py

@@ -520,7 +520,7 @@ def __init__(cls, name, bases, dct):
 
             # parse the XSD file
             cls.logger.debug("Parsing %s and generating classes." % xsdfilename)
-            start = time.clock()
+            start = time.time()
             try:
                 # create nodes for every element in the XSD tree
                 schema = Tree.node_factory(
@@ -535,7 +535,7 @@ def __init__(cls, name, bases, dct):
             # generate attributes
             schema.attribute_walker(cls)
             cls.logger.debug("Parsing finished in %.3f seconds."
-                             % (time.clock() - start))
+                             % (time.time() - start))
 
 class Type(object):
     _node = None