adding a enum class

this might go to a other subpackage later on but for now it
introduces a way to create a "fake" enum. You can pass

a dict or simply keyword aruments:

>>bar = Enum({'a': 1, 'b': 2})
>>bar.a
1
>>bar.b
2
>>bar =Enum(a=1,b=2)
>>bar.a
1
>>bar.b
2
added a Meta class for exeptions

for now its pretty simple but and more of an example how to
assign special exceptions to a class.

from scsi_exceptiom import SCSICommandExceptionMeta as META

class SomeSCSICommand(object):
   __metaclass__ = META