GeezerVison

…umentation (pythonGH-156822)

Corrected, in the documentation and in the docstrings:

* GetInputContext() returns bytes, and its result extends to the end of the
  buffered input;
* Parse() accepts a bytes-like object as well as a string, and ignores the
  encoding declaration for a string;
* ParseFile() only supports binary files;
* XML_ERROR_XML_DECL was described as XML_ERROR_NO_ELEMENTS;
* UnparsedEntityDeclHandler is not restricted to Expat 1.2;
* GetSpecifiedAttributeCount() needs ordered_attributes.

Documented the intern parameter and attribute, namespace_prefixes,
SkippedEntityHandler, XML_CTYPE_MIXED and XML_CTYPE_NAME, and EXPAT_VERSION,
version_info and features.

Removed obsolete notes about Expat 1.2 and 1.95.0, and :noindex: from the
content model constants, which are not documented elsewhere; completed the
list of attribute types in AttlistDeclHandler.
(cherry picked from commit d16a691)

Co-authored-by: Serhiy Storchaka <[email protected]>