Provide a way to customize MARKDOWN2JSON

[UlyssesZh]

For example, to make the tab characters being preserved when using Paru::PandocFilter::Node#markdown=, I have to

Paru::PandocFilter::MARKDOWN2JSON.__send__ :preserve_tabs

This is kind of a hack. What is the correct way to do this?

[htdebeer]

I never thought about preserving tabs while manipulating AST via the convenience method markdown=. I suppose switching that property on by default shouldn't have a negative impact on paru's functioning. But I'll have to look into that to make sure.

Can you given an example where preserving tabs is important?

[UlyssesZh]

In my blog, I use tabs in code blocks and use tab-size in CSS to conveniently change tab size without needing to touch the source files of the articles.

I also wrote a Pandoc filter to transform a code block into some HTML. Whether I use HTML tags directly in Markdown or use raw blocks, the tabs will be converted to 4 spaces. I have to turn on --preserve-tabs.

[htdebeer]

Starting in version 1.2, paru preserves tabs by default. Please test this version to see if it works for your use case.

(Note. I also upgraded the minumum Ruby version to 3.0.6)