lthooks-code: less overfull box

In order to improve the documentation, we do not want to add new
warnings. This is why we try to remove as many of them.
Some code has been reformatted by
- line breaking
- removing spaces
- reseting the indentation
Overfull hboxes essentially come from docstrip's `<latexrelease>`
The documentation is not modified yet.

Update lthooks.dtx

3947, 4138, 5809: no indent reset, replaced by line breaks
5785, 5812 semantic line breaking and format consistency