Add new recursive argument to include directive

[carlocastoldi]

Fixes: #207

Additionally, it also excludes Jupyter Notebooks from the substitution, in case users are using mkdocs-jupyter to import files with very long text as cell outputs

[carlocastoldi]

somewhere, probably, i should write that if this is done to avoid very-long-text substitutions, than the user should use include-markdown.

If you think this can be handy only in this case scenario, i propose to make this directive only for include and swap the order of the substitutions.

[mondeja]

Additionally, would you mind to add tests and documentation? If you think it's too complicated, don't worry, I'll do it.

[mondeja]

This recursive argument must be added to the include-markdown directive as well.

[carlocastoldi]

This recursive argument must be added to the include-markdown directive as well.

Do you see a scenario where markdown recursion might not be desirable, or is that just out of completeness?
I would argue that stopping recursion in markdown is never desirable while it adds confusion on the order of the substitutions now mattering when including very long lines

[mondeja]

I would argue that stopping recursion in markdown is never desirable while it adds confusion on the order of the substitutions now mattering when including very long lines

I don't think that it would add confusion, I don't understand where is the confusion here. Seems to me that it could be useful in certain scenarios, anyways not hurts to add it for completeness.

[carlocastoldi]

I don't think that it would add confusion, I don't understand where is the confusion here. Seems to me that it could be useful in certain scenarios, anyways not hurts to add it for completeness.

This comment shows that it would add confusion, to me: #208 (comment)

But yeah, i'm okay with adding the possibility for markdown too. If you think it's really better. I just wanted to warn you on this