MovableType export: adding comments

I have created a set of patches which allow me to export comments from MovableType site.

The code here adds some IDs to files generated in _posts directory, and also exports comments in _comments directory.

By applying templates and plugin (https://github.com/shigeya/jekyll-static-comments/tree/mt_static_comments) to the output of this modified plugin, I can  statically generate comments to each posts, from the export origin site.