Export html with tags instead of styling when applicable

[donovan-fournier]

This PR updates the formatting of the HTML output.

Before:

• Bold, italic ... were decoded as CSS styling, inline in the "span" tag. This will lose the semantic of these basics tags

After:

• When a matching tag (same as encode), we are replacing the styling by a dedicated tag.

This PR does not handle Header styles as Heading are paragraphs, not spans, and needs a special care.
⚠️ The HTML output is not the same as before, and can be considered as a breaking change
This may address this issue #188 and our own use-case.

[MohamedRejeb]

LGTM! Thanks for your contribution.