Complete and document InsertClassComment().

autoload/PythonDocUtil.vim
	-Complete and document `s:InsertClassComment()`.
Complete PythonDocUtil. Add syntax highlighting.

vim/scripts/PythonDocUtil/ftplugin/python.vim
	-Add syntax matches/highlighting for docstring section
	delimiters.

vim/scripts/PythonDocUtil/autoload/python.vim
	-Fix leading space bug in `s:InsertFunctionComment` and
	`s:InsertClassComment()`.
	-Add file-header documentation.
Remove Sphinx docstring functions.

vim/ftplugin/python.vim
	-Remove the file's obsolete `Sphinx` docstring-generation
	functions.