Merge: Markdown location

Introduce location in markdown parser so tools can easily retrieve the original position of a block or a token in the input file/string.

Commits:
* 2d139eb introduces de Location concept and update the parser
* fda150d isn't interesting since it only update signature in the test file
* dacc7ba adds some test suites for the locations

Pull-Request: #1397
Reviewed-by: Jean Privat <jean@pryen.org>
Reviewed-by: Lucas Bajolet <r4pass@hotmail.com>