Support languages other than Rust for "Hiding code lines"

[ZeWaka]

Note: This is not clearly specified in the documentation that it only works for Rust as well.

Here is the line of code that causes this behavior:

mdBook/src/renderer/html_handlebars/hbs_renderer.rs

Lines 803 to 805 in c83bbd6

	if classes.contains("language-rust") {
	if (!classes.contains("ignore")

Therefore, since the language is not Rust, we execute

mdBook/src/renderer/html_handlebars/hbs_renderer.rs

Lines 851 to 853 in 3f39ba8

	} else {
	// not language-rust, so no-op
	text.to_owned()

instead, leading us to not call hide_lines.

This might just be an oversight.
However, I know some languages would not be happy with this, as they use # for comments.

Therefore, a proper fix for this (imo) would be a configurable BORING_LINES_REGEX, and remove the language restriction.

[baszalmstra]

+1 Would also love to see this!