Strip HTML tags from content sent as Markdown

Strip HTML tags from content sent as Markdown

The "toMarkdown" function prepares content to be sent, primarily, to Diaspora.

The HTML to Markdown converter by default "preserves HTML tags without Markdown equivalents like `<span>` and `<div>.`" At least according to the README in _/friendica/vendor/league/html-to-markdown/_ - which also says "To strip HTML tags that don’t have a Markdown equivalent while preserving the content inside them, set strip_tags..."

Diaspora, however, does not appear to know what to DO with the HTML sent to it. It actually appears to _encode_ the HTML and displays the *code* in the post body rather than rendering it as HTML. In which case it would make more sense to strip out all tags that have no Markdown equivalents.