- xml files are no longer considered harmless
- Factorization of the `remove_all` method for office files
- Explicit whitelist are used
- Blacklist are used to skip files completely
  - Non-blacklisted files are _still cleaned_
  - Unsupported files are still triggering an error

Fedora defines the 'text/xml' mime type for xml files. Adds this mime
type to the harmless parser.

Fixes #36.

Signed-off-by: Antoine Tenart <antoine.tenart@ack.tf>

- the `src` folder is now `libmat2`
- the `main.py` script is now `mat2.py`