Minor documentation updates for eregs clear command

[gregoryfoster]

While reviewing the behavior of the eregs clear command, I noticed two minor documentation updates that can be made.

When running eregs clear --help, I believe the following output refers to a regulation part rather than title on clear.py:19:

$ eregs clear diff/27 trees     # deletes all cached trees and all CFR
                                # title 27 diffs

And in the "Parsing New Rules" documentation's "Fetching the Rule" section, there's mention of a --http-cache parameter which does not look like it's recognized anymore. It looks like the http_client's cache is always cleared on clear.py:31.

I'll return to this and put together a pull request.

[cmc333333]

Good point about http_cache! Regarding title vs. part, diffs are currently stored in a directory-like structure of diff / <cfr title> / <cfr part> / <left version> / <right version>, so I think "title" is correct.

Heads up that the way all of that is stored will be changing soon(-ish) as part of #356. We had a file-system based system for quite a while but are migrating to using Django's models (including proper foreign key dependencies), which should make a lot of this code easier to understand.

[gregoryfoster]

Thanks for the quick response, @cmc333333. My bad re: diff directory structure, I was looking at the output directory structure rather than paths in .eregs_index. And thanks for the heads up re: #356.

[gregoryfoster]

Doc update is in PR #363.

[cmc333333]

#363 resolved, thanks again!