mdstrings support

[luraess]

Trying to add support for mdstrings (introduced in Literate 2.9), I get following warning

julia> serve(clear=true)
  Activating environment at `~/Documents/git/github_vaw/course-101-0250-00/website/Project.toml`
→ Initial full pass...
→ evaluating code [ex2] in (lecture1.md)                                                                              
┌ Franklin Warning: in <lecture1.md>
│ There was an error of type 'ErrorException' when running a code block.
│ Checking the output files '/Users/ludovic/Documents/git/github_vaw/course-101-0250-00/website/__site/assets/lecture1/code/output/ex2.(out|res)'
│ might be helpful to understand and solve the issue.
│ 
│ Relevant pointers:
│ - evaluation of Julia code blocks: https://franklinjl.org/code/
│ 
│ Details:
│ syntax: incomplete: invalid string syntax
│ Stacktrace:
└
→ evaluating code [ex3] in (lecture1.md)                                                                              
┌ Franklin Warning: in <lecture1.md>
│ There was an error of type 'ErrorException' when running a code block.
│ Checking the output files '/Users/ludovic/Documents/git/github_vaw/course-101-0250-00/website/__site/assets/lecture1/code/output/ex3.(out|res)'
│ might be helpful to understand and solve the issue.
│ 
│ Relevant pointers:
│ - evaluation of Julia code blocks: https://franklinjl.org/code/
│ 
│ Details:
│ syntax: incomplete: invalid string syntax
│ Stacktrace:
└
→ Starting the server...
✓ LiveServer listening on http://localhost:8000/ ...
  (use CTRL+C to shut down)

upon non-successful evaluation of a script provided as input to Franklin's \literate{/_literate/test_1.jl} command.

This is coherent with the "wrong" generated script and markdown files before evaluation (see test_1.zip for the input script and the output .jl, .md files).

I tried modifying Literate.markdown() call in src/eval/literate.jl adding mdstrings=true.

It also does not work trying following:

1. add a global page variable literate_md_string in utils/vars with default false
2. in the function literate_to_franklin in eval/literate, get it with mdstr = locvar(:literate_md_string)::Bool`
3. feed it in the Literate.markdown call passing mdstrings=mdstr
4. add @def literate_md_string = true in the page script where \literate{/_literate/test_1.jl} is used