[WIP] Update for spec v0.26

[azerupi]

⚠️ Work in progress, do not merge

This is an effort to update pulldown-cmark to the the latest spec (v0.26). It's not complete and I will probably not have the time and skill to finish this alone, so I thought I would post it so that it could be a collaborative effort.

The test case format in the spec has been modified from

.
<input>
.
<output>
.

to

```````````````````````````````` example
<input>
.
<output>
````````````````````````````````

So I changed main.rs to correctly extract the new format. I wrote an iterator that returns the test cases from the spec and I think it turns out a little more readable than before.

Failing tests

According to the official commonmark tool to test spec compliance, we pass 565/618 tests. But according to the pulldown-cmark test we pass only 504/618 tests. I think this is due to the fact that html is not normalized before testing equality in pulldown-cmark making it stricter than necessary.

Some (a lot?) regressions are du to tab handling. In the new spec some tabs are converted to spaces but some aren't. If I am not mistaken, pulldown-cmark converts all tabs to 4 spaces?

---

If you want to help, just fix some test(s) and create a PR against this PR :)

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[azerupi]

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[azerupi]

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[raphlinus]

Thanks for doing this! I'm short on time right now, so really appreciate people from the community fixing this.

There's one tricky area around deeply nested inline markup. I worked out an algorithm for it, but haven't had time to implement it yet. Probably people should coordinate before taking this on.

[raphlinus]

Thanks for doing this! I'm short on time right now, so really appreciate people from the community fixing this.

There's one tricky area around deeply nested inline markup. I worked out an algorithm for it, but haven't had time to implement it yet. Probably people should coordinate before taking this on.