feat: define md.Content.Headings

[Songmu]

We discussed this in #193 and #194, and I am considering withdrawing the pull request of #194. However, the heading level of the TITLE element in the slide is essential information for determining the layout, so I added it to the property of the Content.

This property itself does not have a particular impact at present, but it should be referenced when implementing the DSL to determine the layout.

The name TitleHeadingLevel may require further discussion.

[k1LoW]

Thank you. I am gradually making progress on DSL as well.

I thought I would record a little more detail, as it seems that not only the heading level but also the number of headings at each level will be important (e.g, Headings: map[int]string{} ).
What do you think?

[Songmu]

Any data structure will fine, It is important that you find it easy to create DSL, so I would like to prioritize your preferences. So I will remake it in that form.

By the way, we could use [6]int or [7]int, but handling 0 is a bit tricky. However, it avoids the problem of random key iteration. It's difficult.

[k1LoW]

map[int]string{} holds the most information. It uses the heading level as the key and stores the title string as the value.

[Songmu]

I see. So you want to enter the title string as is. That certainly provides the most information.

However, would it be okay to use map[int][]string instead of map[int]string for multiple headings at the same level?

Similarly, it might also be possible to use [6][]string.

[k1LoW]

Oh, my mistake. You're right. It should be map[int][]string. Thank you!

[Songmu]

I added md.Content.Headings: map[int][]string. Please review it. @k1LoW

[k1LoW]

It will be helpful!