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
add characters to escape
fix inline-code space-cleaning

fix #78
prevent IDs from being empty

+ better mangling for IDs
fix #63

fix markdown output for code in list items,
by normalising contents of paragraphs
fix list items parsing (#62)

the unindenting algorithm for list items was slightly incorrect,
this commit fixes it. Basically it was sometimes cutting too soon.
add several characters to be escaped when outputing markdown
fix omd_backend.ml+omd_parser.ml

omd_backend.ml:
- improve markdown output
- improve markdown paragraphs

omd_parser.ml:
- add proper escaping for `>` and `<`
fix code block markdown output + fix typo in remove_white_crumbs

properly print the closing when using backquotes
delete last newline in code blocks
Use standard conventions to indicate unused arguments.
Make code for paragraph detection explicit
Add tests for the AST of Markdown lists.