refactor disqus migration code into a class
replace assert with assertEqual
add initial support to import WordPress comments
Disqus import uses Progressbar class as well
disqus import imports anonymized IP address now
update docs
handle WP's query-string "pages" and variable WXR namespaces

Site links such as /?p=1234 are imported *as is* and maybe do work in
Isso. Do not use a query-based URL structure as permalinks. Ever.

Also, depending on the pages you are going to export, WXR' XML namespace
may change from ../export/1.0/ to ../export/1.2/. Isso tries to import
any WXR 1.x
Merge branch 'feature/75', closes #75