Merge pull request #81 from Chris00/master

Remove newlines at the end of list items + tests
fix markdown output for undefined references

i.e., do not escape brackets when using the fallback text
loosen comparison a little more for references

if 2 references are the same except for their fallback texts,
which differ only by one having a [] suffix while the other has not,
then they are considered as the same.
remove `NL` preceding blocks (in `normalise_md`)
Always use the fallback text when outputing markdown for references
loosen `loose_compare` for code blocks

if 2 code blocks only differ by a `\n` at the end of one of them,
then they are considered the same.
omd 0.8.0
improve documentation
fix: non-valid HTML tags were not correctly parsed

some parts were accidentally dropped!
`make_paragraphs`

- making paragraphs is no longer optional
  (command line option `-P` has been removed)
- function `make_paragraphs` has been moved from Omd_backend to Omd_parser
- `normalise_md` has been moved to Omd_representation
Add class to `pre` for code blocks + add class to inline code

(Concerns HTML output only)

- Code blocks now use the attribute `class` for both tags `pre` and `code`
(fix #57)
- Inline code now also use the attribute `class` when it's relevant.
fix: make testing process use Omd_representation.normalise_md instead of Omd_backend.normalise_md
fix wrong parentheses

some parentheses were wrongly used in inline html parsing
Add test for 2 levels list.