Fix markup used in the documentation of sys.prefix and sys.exec_prefix.
Fix markup used in the documentation of sys.prefix and sys.exec_prefix.

- Using the file role with {placeholders} is IMO clearer than fake
Python code.

- The fact that sys.version[:3] gives '2.7' is a CPython detail and
should not be advertised (see #9442), even if some stdlib modules
currently rely on that detail.

sk-/python2.7-type-annotator,sk-/python2.7-type-annotator,sk-/python2.7-type-annotator