remove <br/> at the end of paragraphs
fixes

- markdown output of blockquotes
   (was not correctly indented when in list items)
- remove newlines and BRs at the beginning of paragraphs
+ val loose_compare : t -> t -> int

(it's not a strict compare, hence the name)
fix markdown output for img references + quick escape fix

- alt and name were (wrongly) swaped in the output

- we need to escape some characters when we output markdown, such as
  dots, dashes, stars, etc. Over-escaping is ugly but semantically
  correct, and that's what's done for now. Need something better but
  later...
new file: tests/cow/code-block-vs-setext-titles.html

reason: was missing.
add Omd_backend.normalise_md
fix: remove the first extra newline of a blockquote

reason: it's generated by the parser and it messes up the markdown output
fix testing files