About .dll location, I have nothing to say: it's allright like it is (IMO)

But I think all the docs should be placed in the same folder. About modules coming with several .txt files: a readme, a changelog... I think all the stuff should be in the readme file to allow having only one help file per module.

About html files, stuff could be organized like this:
- modulename.html
- modulename.css (hidden)
- modulename-pic1.png (hidden)
- modulename-pic2.png (hidden)
- ...