Generalized the Codebraid support to MkDocs

[reenberg]

In #57 support for Codebraid syntax was added, which essentially is just Pandoc attribute syntax, but with a specific class attribute added.

The support was added as an extra identifier in the list of languages, for which Codebraid has support, such as for python: \\{\\.python.+?\\}.

The below example would give the following scope: "text.html.markdown markup.fenced_code.block.markdown fenced_code.block.language.markdown" to the entire line:

```{.python .cb.nb jupyter_kernel=python3}
```

However the "language scope" should only be given to the "python" part, and the current support doesn't allow spaces between the curly braces, and it lacks support for all languages.

MkDocs allows a few ways to annotate fenced code blocks, but if additional classes, id or key/value pairs are used, then the curly braces must be used and the language must be prefixed with a dot. In simple cases where only the language is specified, then the curly braces and the dot may be omitted. The following are quick examples:

``` { .python #id .class title="My Title"}
```

or

``` python
```

This change removes the Codebraid support from the specific languages as an identifier attribute, and moved into the RegEx by defining it as two alternative cases: surrounded by curly braces or allowing them after the language:

1. The case where the entire line after the code fence is wrapped in curly braces. In this case the curly braces is not part of the language and attribute scope.
2. The case where the attributes follows the language specification in all sorts of ways (I'm specifically thinking of you Gatsby Adding attributes to fenced markdown code blocks breaks syntax highlighting #62). In this case the curly braces are included in the attribute scope as it is not trivial to handle all the various ways it may be used, and since this is the current behavior.

@microsoft-github-policy-service agree

Closes #153
Refs: https://github.com/Python-Markdown/markdown/blob/master/docs/extensions/fenced_code_blocks.md

[reenberg]

@microsoft-github-policy-service agree

[reenberg]

It would seem that this PR also has the side effect of fixing the broken Codebraid support for Rust, which was mistakenly matched as R code. This is most of the changes in the file pr-57_md.json. The rest are basically just updates to the fenced block not correctly scoping the language and attributes.

[reenberg]

@mjbvz, @alexdima, any chance this can receive a review and be moved along?

[rzhao271]

Moving the milestone
Also, there are merge conflicts

[mjbvz]

Can we break this up into a multiline regular expression. It was already a bit long but now it's unreadable

[reenberg]

Ill see if I can find time to setup another dev environment to properly test out the changes that this will include.

[reenberg]

Moving the milestone Also, there are merge conflicts

There would have been no conflicts if this had not been ignored, until way after a MS employee merged other changes (#158), ignoring all other PRs!

I will try and see if I can find the time. But its about 5months since i invested time into understanding this set of fairly complex expressions. not to mention setting up a dev environment to test this, in order to implement the suggested changes.