Add configuration option to disable the default hidelines feature for rust

[zgtm]

Simple change that adds a configuration option to disable the default hidelines feature for rust:

Usage:

[output.html.code]
default-hidelines = false

I need this in my book since I have several multi-line strings that have lines starting with #. (Embedded code snippets with preprocessor directives.)

Let me know if this needs a test.

If you want I can also add a line to the manual, but since this is a niche feature, the doc string might just be enough. :)

[Edit: Added a test]

[max-heller]

I need this in my book since I have several multi-line strings that have lines starting with #. (Embedded code snippets with preprocessor directives.)

You can use two consecutive hashes ## to keep the line visible.

[zgtm]

Hi @max-heller, thanks for the hint!

Unfortunately this will not work in my case, as I'm trying to include the code from a source file via {{#include filename}}, and the source file will only work with this particular line starting with a single '#'.

(One could argue whether the line hiding mechanism should be disabled completely for included sources via {{#include filename}}. But I did not want to open that can of worms. 😬)