Implemented rusty error handling as #176
Something may be still rustified in
src/header, but I think this could be already merged to have a starting point.
One thing to do could be to get rid of the
into_posix_style() used by
src/fs.rs and by
src/platform/mod.rs. A way to handle the errno there is to be find, since nothing is returned by the former and
fmt::Result by the latter.