Skeleton implementation

no documentation at all.
can we simplify this part?
```python
for required in ('id', 'properties'):
    if required not in skeleton:
        raise SkeletonException("missing '%s' field" % required)
for field, reqtype in dict(id=basestring, description=basestring, allowUpload=bool, properties=dict).items():
    if not isinstance(skeleton[field], reqtype):
        raise SkeletonException("field '%s' must be of type '%s' % (field, reqtype.__name__))

self.id = skeleton['id']
self.description = skeleton['description']
self.allowUpload = skeleton['allowUpload']
props = skeleton['properties']
```