Hide code lines with #hide when executing Markdown

[devmotion]

This PR fixes a surprising behaviour that seemed a bug to me, both intuitively and after reading the documentation. Feel free to close the PR if it is intended and there is another way to achieve the same behaviour 🙂

For different reasons, I would like to execute a Documenter-flavored Markdown file generated with Literate with Literate instead of Documenter. However, as with Documenter, I would like to suppress the output of lines that end with #hide in the final file. To my surprise, currently this does not work:

julia> using Literate

julia> write("literate_script.jl",
       """
       a = 2 + 2
       print("a: ", a); nothing #hide
       """);

julia> Literate.markdown("literate_script.jl"; execute=true, credit=false);
[ Info: generating markdown page from ~/literate_script.jl
[ Info: writing result to ~/literate_script.md

julia> print(read("literate_script.md", String))
```@meta
EditURL = "<unknown>/literate_script.jl"
```

````julia
a = 2 + 2
print("a: ", a); nothing #hide
````

````
a: 4
````

Including this file in a Documenter setup doesn't help either since Documenter does not remove lines in julia codeblocks (only in @example AFAIK).

With this PR the line is removed from the resulting Markdown file but, of course, still executed. Hence including it in my documentation yields the same output as if I would have executed the Markdown file with Documenter instead of Literate:

julia> using Literate

julia> write("literate_script.jl",
       """
       a = 2 + 2
       print("a: ", a); nothing #hide
       """);

julia> Literate.markdown("literate_script.jl"; execute=true, credit=false);
[ Info: generating markdown page from ~/literate_script.jl
[ Info: writing result to ~/literate_script.md

julia> print(read("literate_script.md", String))
```@meta
EditURL = "<unknown>/literate_script.jl"
```

````julia
a = 2 + 2
````

````
a: 4
````

@racinmat noticed this inconsistency in #166 (comment) as well. I checked that the example there is fixed as well, with this PR the code block is shown as

[devmotion]

What's your opinion @fredrikekre? Do you think the PR is a good idea?

[fredrikekre]

Yea this seems fine, it is a bit difficult to understand all the combinations of options at this point, sadly.

Can you add a note in the CHANGELOG.md?

[fredrikekre]

Can you also add a test case for a statement which ends with ; to test https://github.com/fredrikekre/Literate.jl/pull/188/files#diff-77ef252c95f9f0ebed0b4f907d587a7ed768e258e8ac5338650569a914bc4c58R539 ?

[devmotion]

I added a test for 123+123; (which was already part of the test) that checks that no nothing #hide is added. I hope this was what you had in mind.

[fredrikekre]

Thanks!