Validity of the generated HTML

[kukimik]

At #216 I reported a bug: there is no DOCTYPE declaration in the generated HTML files.

This is, however, an element of a wider problem: are the generated files valid HTML5? This should ideally be checked using some validator.

For example the Nu Validator (https://validator.w3.org/nu) applied to https://note.ema.srid.ca/index.html reports missing alt attributes in images as errors, and also warns about the superfluous type='text/css' attribute in the <style> tag. (However, to run the validator, you have to remove <head-main></head-main> from the source, because it somehow breaks the validator's parser.)

I know a test suite (#152) is planned. Perhaps this should be one of the things that are tested.