Added a new backend: libarchive-c

Use the wrapper from: pypi.python.org/pypi/libarchive-c

This new wrapper are the best I have tryied so far, they are really simple and works with py3,
next step is to include the wrappers directly inside the epack source code so tht we don't relay on
external tools (there are too many libarchive implementation and it's quite impossible to discriminate which one you have). Once we will have them inside the source we can safetly remove of all other backends