ataru can handle multiple files and test methods are named after md files

- Now, ataru can handle multiple files:

```bash
$ ataru my_file.md my_file_2.md
```

- Test method names contain the filename of the markdown file.
This is just to be considered as some sort of random fact :-)

The number to be used when exiting a program are somewhat [well defined](http://stackoverflow.com/a/1535733). In this case you should return 64 (command line usage error) if no argument was given, 65 (data format error) if the file is not in Markdown format and 66 (cannot open input) if the file could not be found.

But at the same time you already differentiated between all those cases, which is very well done.