Implement psr4

[valentintorikian]

I've implemented the composer's PSR-4

• The directory structure is pretty different, but I think that it convey your initial intentions pretty well
• The tool is now started through bin/mar.php, this way we avoid the definition + initialization of the class in the same file, options are unchanged

[Alexia]

I am not really sure it is necessary to move the main executable in a subfolder. However, I do see it is not PSR-4 compatible due to the lack of a vendor namespace. I will look at this later on.