Add sysfs_path returning &Path, deprecate path()

[Dirbaio]

Currently you can get a SysfsPath from DeviceInfo, but you can't really do anything
with it because it has no methods and the inner PathBuf is private.

This makes it pub.

The SysfsPath type is a bit useless from outside the crate though. Alternatvely DeviceInfo.path() could return a PathBuf, but that's a breaking change.

[kevinmehall]

How about adding a new method DeviceInfo::sysfs_path(&self) -> &std::fs::Path and deprecate path() to be removed in 0.2? path is kind of a bad name anyway, because it could be confused with the /dev/bus/usb path to the device node.

Anyone using this is probably going to reimplement the private methods on SysfsPath for reading sysfs attributes, but I think exposing those is probably beyond the scope of this library, so Path or PathBuf is probably better than having an extra type in the API.

[Dirbaio]

@kevinmehall sounds good, done!

[kevinmehall]

Thanks!