A few new docstrings.
Avoid using shell metacharacters in output filenames.
Show a crude progress indicator when splitting an archive.
Add & use DATE-SORTED-ARTICLE-IDS.

Getting the date for an article is a little indirect, so when sorting
a sequence of article ids by the date of the article, it can be
batched up a bit.
More documentation in SEARCH-RESULT-PAGE.
Create the term id CDB file on demand.
Article retrieval: functions for first, last, next, previous articles.
Starting to export the intended interface.