Skel fixes

[rprimet]

This is a PR to fix #45

• [X] The number of # in front of the headings should be nesting_level + 1, the + 1 is because we have a first title for the code (# Code des impôts) -- needs testing though, throughs mocks for now?
• [ ] Some headings are in bold ( ... ) in markdown, I don't think we should keep that
• [x] The newlines in the text of the article are not preserved by catleg skeleton but they should, a newline on LégiFrance should be \n\n in the output of catleg skeleton.
• [X] When the NOTA is empty, don't print NOTA
• [X] The NOTA: should be with the following format: \n\nNOTA :\n\n

Note unit test failure on Windows needs investigating: encoding?

[rprimet]

Hi @denismerigoux, I think this is ready for review ; it includes most of the fixes that you mentioned except for the italics in some titles (after checking, it was part of the text in the Legifrance headings -- if you think we still need to strip those, can you open a separate issue?)

I'd rather get this merged if it helps making a small step forward as I may have little time for the next 1-2 weeks, so I'd rather make a small incremental progress than wait. WDYT?