FEATURE: add multidevice support

[bpereto]

This adds multi-device support, in case you have multiple LUKS-Devices, which are needed to handle at boot-time. Basically it loops over the given devices in the config-file and applies the mechanism already in place.

To configure, add the devices sepparated by a space to your configuration section:

[general]                                                               
device name = crypt crypt2

Would resolve #14 .

Any suggestions? (I don't know how to resolv the magic number).

[eworm-de]

What happens if an error occurs half way through the process?