Better definition for xml/sax/__init__.pyi. (#621)

Also, merge 2.7/xml/sax and 3/xml/sax into 2and3/xml/sax.

stdlib/2.7/xml/sax/__init__.pyi

@@ -1,20 +0,0 @@
-# Stubs for xml.sax (Python 2.7)
-#
-# NOTE: This dynamically typed stub was automatically generated by stubgen.
-
-class SAXException(Exception):
-    def __init__(self, msg, exception=None): ...
-    def getMessage(self): ...
-    def getException(self): ...
-    def __getitem__(self, ix): ...
-
-class SAXParseException(SAXException):
-    def __init__(self, msg, exception, locator): ...
-    def getColumnNumber(self): ...
-    def getLineNumber(self): ...
-    def getPublicId(self): ...
-    def getSystemId(self): ...
-
-class SAXNotRecognizedException(SAXException): ...
-class SAXNotSupportedException(SAXException): ...
-class SAXReaderNotAvailable(SAXNotSupportedException): ...

stdlib/2and3/xml/sax/__init__.pyi

@@ -0,0 +1,32 @@
+import xml.sax
+from xml.sax.xmlreader import InputSource
+from xml.sax.handler import ContentHandler, ErrorHandler
+
+class SAXException(Exception):
+    def __init__(self, msg, exception=None): ...
+    def getMessage(self): ...
+    def getException(self): ...
+    def __getitem__(self, ix): ...
+
+class SAXParseException(SAXException):
+    def __init__(self, msg, exception, locator): ...
+    def getColumnNumber(self): ...
+    def getLineNumber(self): ...
+    def getPublicId(self): ...
+    def getSystemId(self): ...
+
+class SAXNotRecognizedException(SAXException): ...
+class SAXNotSupportedException(SAXException): ...
+class SAXReaderNotAvailable(SAXNotSupportedException): ...
+
+default_parser_list = ...  # type: List[str]
+
+def make_parser(parser_list: List[str]) -> xml.sax.xmlreader.XMLReader: ...
+
+def parse(source: str, handler: xml.sax.handler.ContentHandler,
+          errorHandler: xml.sax.handler.ErrorHandler=...): ...
+
+def parseString(string: str, handler: xml.sax.handler.ContentHandler,
+                errorHandler: xml.sax.handler.ErrorHandler=...): ...
+
+def _create_parser(parser_name: str) -> xml.sax.xmlreader.XMLReader: ...