[O] [ANN] Markdown export back-end in contrib

[Nicolas Goaziou]

Hello,

I introduced a Markdown export back-end in contrib/.  It uses atx syntax
for headlines and inline syntax for links and images.  It is quite
simple, so don't expect much about it.

This is Markdown vanilla flavour, so there are a few thing that it
doesn't support.  Among them, some are simply ignored (i.e. footnotes),
other are sent to HTML back-end (i.e. tables).  Anyway, creating a new
flavour out of it (i.e. Github Markdown Flavour) is simple with
`org-export-define-derived-backend'.

You can use `org-md-export-as-markdown' and `org-md-export-to-markdown'
functions to test it.

Feedback is welcome (note: I don't use md format, so for suggestions,
please be explicit).


Regards,

-- 
Nicolas Goaziou