`data` argument does not work

[lrq3000]

Hello there,

When using the data argument to initialize the chest with a dict, it seems the inmemory dict does not get correctly initialized. Here is an example:

out = Chest(data={'id': set(), 'label': set()})
out2 = Chest()
out2['id'] = set()
out2['label'] = set()
print(out.keys())
print(out2.keys())

Output:
[]
['id', 'label']

When data is used, the keys are not available, as well as hasattr(out, 'id') will return False, but out['id'] will work and return set().

BTW, it is also not possible to update a chest with a simple dict:

out.update({'id': set([1, 2])})

Output:
---------------------------------------------------------------------------
AttributeError                            Traceback (most recent call last)
<ipython-input-76-7a010f35ab01> in <module>()
----> 1 out.update({'id': set([1, 2])})

C:\git\centertbi-mri\libs\chest\core.py in update(self, other, overwrite)
    290         #  if already flushed, then this does nothing
    291         self.flush()
--> 292         other.flush()
    293         for key in other._keys:
    294             if key in self._keys and overwrite:

AttributeError: 'dict' object has no attribute 'flush'